That's weird.  I'm running close to the exact same system, and Carrara 8 pro 64 does fine for me. I have Windows 7 64, 8 gig, quad core, GeForce GTS 250 NIVIDIA card.  (!?  The video card is the same?!)  Processor is an AMD Phenonom II X4 95 3.21 Ghz.

Wonder what's going on?  Hey, what kind of virus software do you have?  I use Kaspersky.  Did you give Carrara administrator privledges?  I know you've probably done this, but have you tried running it with the antivirus turned off?  Some programs do not play well with others.

Does tend to crash a good bit, which is annoying.  I just save often.