There are only two cards that can fully support DX10. The Nvidia 8800 GTX and GTS. ATi will be coming out with their DX10 cards shortly.
The 7900 can run Vista but it cannot play games using DX10. That is not to say it can't play the games at all. I believe the games will still be able to run using DX9, but not with all the new eye candy of DX10.
Hope this helped some.