Those choices will not disappoint you, your current computer will work in Vista.
the 8800GTS is a great card, but its current DX10 performance is a bit iffy. If you can go for the GTX.
Your 7950GT will work fine in vista, it just won't support DX10 (Only like 4 DX10 games exsist, and they have bad performance on any computer)
Also i'd get the mobo fatality linked instead.
Sorry to disappoint you but the G92 chip is the 8900GTX and the 8950GX2, not the 9XXX series. Many people have this confused. The G92s will be released sometime around november, while the 9XXX series will be release mid-late 08. I can see waiting for the 8900GTX, but waiting for the 9800GTX is a bad idea because its a year or more away.
Also the 9800GTX series most likely will be named something completely different.
And I can tell you right now that those specs are incorrect as well. As for my source? I cannot say that because I have a inside source.
Everything related to the 9800GTX currently is false.