but check this ...
upgrading to windows 7 gives you some new graphic eye-candy abilities.
i dont know if the directX 9 games use those new abilities though.
to say the least, it would appear the new operating system allows a speed increase to provide some room for those new eye-candy abilities.
Games can only use DX10 and DX11 effects if they have been designed to use those effects.
For example, Mass Effect 1 & 2 are DX9 games. Playing those games in Win Vista or Win 7 will not automatically improve graphic effects.
Crysis 2 was initially released as a DX9 title on the PC. You need to install the DX11 patch to upgrade the game to use DX11 effects. The patch was released 4 months after the release of the game.