Demo played fine, full game crashes (windows 7, naturally)

[Pezofdoom]

So, I posted the whole issue over in the steam forums but then I realized it'd probably be smarter to just come to the actual support forums and ask.

Full info with system specs and troubleshooting steps already taken:
http://forums.steampowered.com/forums/showthread.php?t=2705569

Anyway, it seems that a lot of people had this issue possibly because of the age of the game vs. some updates to technology.

Would you recommend downgrading from direct X 9.0c to an earlier version?  I saw in the sticky that you mentioned something about attempting to run a 2008 to workstation directmusic program, but I am not entirely sure that'd be a good thing to run on my windows 7 ultimate OS.   

Did the demo run fine because it's an earlier build of the game than the full version?  Any suggestions would be good, I'm just really excited about playing such a wonderful game fully through.

[Pezofdoom]

Update:  Solution found.  Turns out AVAST Antivirus freaks out on the full version of the game.  I disable the AV client and it runs fine.