When is the next generation of video cards scheduled for release ?

Later in this year i think we're getting new stuff. Q4 i think, which corresponds with Windows 7 and DirectX11's release.

So is windows 7 going to be like vista ? Meaning dx11 is only useable on windows 7 or will vista users be able to download dx11 drivers ?

There are a lot of rumors about nvidia's gt 300's as of late. I think they may be out sooner than people think. August September maybe! They are going to want to get these new cards out soon to take advantage of the windows 7 release. Many new computers will be purchased when windows 7 comes out.

vista users willalso get DX11, though after win7 is already out.
The DX11 gpus will be released between Q4 2k9 and Q1 2010

DX11 is only a superset of DX10, and will be fully compatible on any DX10 OS, or Vista and W7

DX11 is available on vista SP2.

and I think you didn't remember that win7 is vista sp2 with some add-ons.

Not to mention some current (ATi) cards are already DX11 capable since the architecture is so similar to DX10.1.