I haven't tried it yet, but an alpha release (lol Microsoft Alpha...) is here if anyone's brave enough to give it a go:

http://www.mediafire.com/?0didxs1dbpz

what would this add?

better performance of DX10 compatible games, assuming you have a supported video card.

ooh gotcha.

Umm, hate to bust your bubble Yoda, but we have actual confirmation at TF that some people HAVE gotten it to work.

http://www.tech-forums.net/pc/f9/directx-10-windows-xp-download-157671/

http://www.technospot.net/blogs/download-directx-10-for-windows-xp-from-alky-project/

Those are unofficial, messy hacks, that prolly cause more problems than anything, show me a technet link...

[edit]

I made my Voodoo3 work with DX8 with simaler hacks, in Windows 95! But Microsoft themselfs ARE NOT releasing DX10 for XP, cos there IS NO DX10, Its Direct3D 10 :P

[edit 2]

Oh yah, I always take forum posts and blogs as gospel, just like Wiki's.