I purchased the game through Steam, and now everytime I try to run the game it crashes. I try to run it, and the screen goes black, then just stays black. Once I move the mouse, however, it stops working and I get a fatal error comment. I looked through the forums, and nothing I found through there works. I diabled my firewalls and made sure that it was running as admin. I was able to run the demo after changing the Compatibility mode over to Windows XP, but doing that does not run the full version. I have tried reinstalling it, to no avail. Any suggestions?

P.S. I am also running on Vista, if that helps.

No it doesn't... in fact Vista is most probably the cause!  ;)

Try the usual: Run as Administrator.
If that doesn't work, not a clue. XP & Linux person myself...  8)