Don't know if this has been posted yet but DirectX 11is out for Vista on Windows update. The catch is because you have to run a script that changes some registry values reboot and then go to windows update then the update will show up. I believe you to do this because Win7 is not out yet and Microsoft won't release the pacth till then?
Anyway gave it a try last night and it works, ya I know my vid card is only DirectX 10.1 I was bored

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Note:
This is not an DirectX 11 install package that was floating around the web, it is available on Windows update,
do not I repeat dot not download any DirectX packages from the net other than from Microsoft as there has been some that were fake and contained viruses.