I'm not sure about the 8800 cards. You will have to run Vista to get the most out of them. There aren't any decent games for DX10 yet. One of the guys in the clan has a PC running Vista, he has a pair of 8800. He is getting lower fps under Vista playing BF:2 than I am with XP with just the one card and a single core CPU.

I figure you have to get what you can afford at the time, the prices change so much, by the time you have saved enough for what you want, what you want has changed...