This is weird news because I just read on I think Tom's Hardware site a couple of days ago that MS wasn't going to release DX11 for Vista untill much later, like Service Pack 3 possibly.

But today Anandtech posted :
DirectX11 Released For Windows Vista

The update is KB971512, which is being released as part of a larger Platform Update for Vista that includes a few other things that are being backported for Vista. Vista SP2 is the prerequisite, so if you aren’t already on SP2 you’ll need to update.

All of these updates should be available on Windows Update.

Really though, it probably isn't worth installing right away since I don't think any of us have a DX11 card yet (only ATI has them out, and they are very limited in quantity, nor are their really any games to use it with ). I'm going to give it a few days and see what other folks are saying about the update to make sure everything is working right, then might give it a go.

I will say I'm already tired of all the commenter on sites like Engadget that see the comparison shots between DX10 and DX11 and then talk smack about it being a waste because you can barely see a difference. The point of DX11 is more about performance than eye candy (though there is some of that). The stuff it allows devs to do means they can put in the same amount of eye candy in top end games now, but your computer will have less stress and run at higher FPS.

For instance, check out this Tech Video from the new DX11 Dirt 2.
DiRT 2 DirectX 11 Tech Video HD

That is in HD and downloads really fast.

If you can't download it, I found the tiny streaming version, but it really just doesn't do it justice.
Streaming
DiRT 2 trailer races to show off DirectX 11 features

Also check out:
Why DirectX 11 will save the video card industry and why you don't care



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