Well I play GTR2 and GT Legends and I got Race 07 last Friday and first thought it seemed fairly good a lot better the Race 06 which I have but never play. So as with a lot of people I was getting a lot of stutters while playing it spent hours trying to find a good set up and still not happy so I finally chose to install XP 64 and guess what no stutters in fact it runs very well it does use up more system resources then GTR2 and Legends but under XP there are no problems.
I like Vista and have been using for 6 months now but even I have giving up on waiting for something or someone to make it work properly and the real said truth is after being away from XP 64 for 6 months all my games feel like Iíve just bought a new graphics card.
Processor: Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz (2 CPUs) set to 3.20GHz
Can't help you directly but I'm running a near identical setup to you (E6600@3Ghz, 4GB RAM & 8800GTS @1680x1050) on Vista 64 and it is as smooth as silk. I have not seen any stuttering in RACE07, GTL or rFactor.