The Inquirer has an interesting article about something called the Alky Project which claims to have initial support for DirectX 10 on Windows XP (and possibly other operating systems).
The Inquirer article is here (it links to a number of bits of info about the project):
http://www.theinquirer.net/default.aspx?article=39095
They've released some sample DirectX 10 DLL files here:
http://fallingleafsystems.com/site_media/preview.zip
which they claim support at least one of the DirectX 10 demos fairly well (there's a readme in the zip, which is small, only 824k).
I see that some person with an interest in WINE has already asked about this, to make sure they're not ripping off WINE, and they've responded with some details (including a bit of code) here:
http://www.fallingleafsystems.com/forum/index.php?showtopic=12
Just posting this in case any developers haven't seen this yet and would like to know about it - sorry if it's just repeating stuff you already know, but I couldn't find anything in wine.devel about it.
Best wishes
Ian Macfarlane (I'm not affiliated with any of the stuff mentioned in this email)