Mac OS X Lion is 64bit ONLY... so if your drivers (kernel extensions) aren't ready for 64bit then they likely won't work in Lion.
If you are running Snow Leopard and want to boot up with the 64bit Kernel (Most SL installations default to the 32bit Kernel) you hold the "6" and "4" key on the keyboard during boot.
This will let you know what does and does not work in the 64bit environment before you upgrade.
Here's an
article I found quickly on Google that details this a bit more.