Service Pack 1 can use DirectX 10.1 and those without SP1 will use DirectX10.
DirectX 10.1 adds specifications that were optional in DirectX 10, like 32-bit FP filtering.
The next generation games based on DirectX10.1 will provide a new level of graphics quality. Currently, ATi has released graphics cards based on DirectX 10.1, but the games to utilize the features are yet to be built.
Currently, the DirectX 10.1 is under Beta Testing along with Vista Service Pack 1 and it would be available in the early quarter of 2008. There are rumors that
Microsoft is trying to make DirectX 10.1 compatible with XP.
Gaming enthusiasts and freaks who've spent hundreds of dollars buying the top of the line graphics cards need not worry as the DirectX 10.1 games will function on
DirectX 10 cards, but will not look as good as on a DirectX 10.1 card. None of the 8800s and 8600s that gamers have bought so far will DirectX 10.1 based games the way they should be run.
Let’s wait and see until it is finally out!

