Have used Vista for a while and didn’t have any problems.
Only thing i have done was disable UAC (the administrator thing)

And i didn’t use bitdefender from MS.
All that kind of build in stuff i didn’t use.
If you use the standard virus scanner and such, wich comes with the vista install that can give problems.

What you also can try otherwise, run it in compatibillity mode:
Windows XP SP2.
Freelancer & Modmanager.

You sure you also have the good drivers for your graphic card?