Well... I'm stuck at DX9 on XP... I am anxious to see what DX10 offers in Windows 7 with my current 8800... Will it be able to take advantage of DX11?
As was stated, Windows 7 is DX11 as is Vista now. As long as you have a DX11 Compliant video card, you'll do fine. For a lot of bang for the buck, an ati HD5770 is a good card as long as you have a decent PSU.