Hauppauge have at last released beta drivers to try and fix the stuttering that affects MPEG captures on Windows XP. Haven't installed them yet myself (I'm at work..dammit), but I thought I'd let people know so you can try them yourself. I think they are still VFW drvers rather than WDM drivers but as long as they work I don't mind.

http://www.hauppauge.com/html/sw_pvr_pci.htm#2000