USB 2.0 support for Windows XP may have escaped from Redmond slightly early, in accordance with a long tradition of such breakouts. A USB 2.0 patch is due out via Windows Update and hardware vendors later this month, but something that certainly looks like it is currently available for download at littlewhitedog.com.
As Fido at Littlewhitedog says: "I will probably wake up the morning and have to take this down, but what the hell I've got a chance to help out a few people with this one." Indeed - maybe yes, maybe no. The file, Q312370_WXP_SP1_x86_ENU.exe, looks plausible, although The Register hasn't yet been able to test it with USB 2.0 hardware. Given that Microsoft intends the patch to be out this month, our guess is that the software is finished, being checked by hardware manufacturers, and that's where it leaked from.
The Microsoft knowledge base article to match Q312370 seems not to exist yet, but the SP1 designator would signify that it's being viewed by Microsoft as a pre-WinXP SP1 patch that will be rolled into SP1 when it ships. It's also possible that it's now available via one of Microsoft's 'special' distribution systems for corporate customers; this has been a common route for previous escapes. ®