I don't use the program personally. I've never heard of it untill now, but it looks like an interesting program. A quick search around finds that if you give the program shortcut Admin Privledges, and run it in "Windows XP SP2 Compatability" mode... it should run the program fine. Sadly though, realtime video preview doesn't work... and you have to export the vid in order to see. Seems kinda like a waste of time... but hey, go for it.
Vista seems to f*ck everything up doesn't it?
EDIT: I was just searching over the AVID website and found that you can upgrade to Avid Media Composer (which is the new Avid Xpress, apparently) for about $400USD. Seems a little pricey, but if you've got the money, it may help your compatability woes.