Your site has some invalid markup which might be causing some issues, the main one I see just glancing through is that you have a body tag down by the slider code then another below the head.
I think you can get this to work by forcing the first li to position top and left 0px, I added the code. It works in firefox/firebug, but you'll have to try it on your site to see. Basically when the plugin is firing it is assigning position absolute to the all the li's but doesn't apply a top and left to the first "slide".
look for this code change below...
<li style="position:absolute;top:0px;left:0px;">
Code:
<[SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]body[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]> <---- this shouldn't be here[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]id[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="slider">[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]ul[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]style[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="list-style: none;">[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li style="position:absolute;top:0px;left:0px;"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]img[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]src[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="slideshow_images/pic1.jpg"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]alt[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="Engine"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]/>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]style[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="padding: 0; margin-top: 0;"></[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE]
[SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li>[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]img[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]src[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="slideshow_images/pic2.jpg"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]alt[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="Engine 2"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]/>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]style[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="padding: 0; margin-top: 0;"></[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]img[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]src[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="slideshow_images/pic3.jpg"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]alt[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="Engine 2"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]/>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#ff0000][SIZE=2][COLOR=#ff0000]style[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]="padding: 0; margin-top: 0;"></[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]li[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]ul[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]Engines[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]h3[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]<[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]pre[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2]$(document).ready(function () {[/SIZE]
[SIZE=2]$("#slider").simpleSlider({[/SIZE]
[SIZE=2]width: 486,[/SIZE]
[SIZE=2]height: 196[/SIZE]
[SIZE=2]});[/SIZE]
[SIZE=2]});[/SIZE]
[SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]pre[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]></[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]div[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]</[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]body[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]>[/COLOR][/SIZE]
[/COLOR][/SIZE]