No idea on trying to run it on a virtual machine session. Personally I'd not try it myself as you do not want a "buggy" or otherwise rigged setup for business critical things. Also versus downloading drivers from some third party site I'd suggest downloading them directly from Mimaki.
http://www.mimaki.co.jp/english/download/uc_index.php
Not saying they are (and they are probably just fine) but who knows if someone has tampered with files from 3rd party sites. If you can get something directly from the manufacturer it just seems prudent to do so.
Not really sure what version the driver at the other site is but the newest 3.0 one from Mimaki also supports 64 bit operating systems if the copy of
Windows 7 you will be using is 64 bit that will be mandatory.