Bartacus
BartWatch
I wouldnt be too quick to blame 64 bit Vista. I'm running an 8800GTX with 4 gig of RAM on Vista Ultimate (64 bit) and Gothic 3 plays perfectly. I've jacked up all the view distances and cache settings as well.
The only issues I've experienced were Nvidia driver crashes, but only in LOTRO at this point. Once every few days, so I'm living with it. Its always the WHQL driver that does it.
I blame vista 64b -> I recently installed win XP on my new pc and it plays way smoother then on vista. I did change the view distances too.(I like a larger camera distance and it's not very good when the character gets out of sight)
my specs are 8800GTS 512MB (= equal to your card), 4GB RAM and the 8400 Intel dual core cpu.