The drivers will "probably" exist but it's finding them that can be a chore. Open the Device Manager while Vista is installed and write down all the current drivers and device names so you can find them BEFORE attempting the XP installation. See the links below to read about others who have "downgraded" to XP with other computers:

HP Computers Mainly
http://forums.cnet.com/5208-12546_102-0.html?forumID=133&threadID=243153&messageID=2460401

General Guide
http://forums.cnet.com/5208-12546_102-0.html?forumID=133&threadID=238817&messageID=2487295#2487295

Dell Computer
http://forums.cnet.com/5208-12546_102-0.html?forumID=133&threadID=259474&messageID=2557700

Gateway Dual Boot
http://forums.cnet.com/5208-12546_102-0.html?forumID=133&threadID=259200&messageID=2556095

Toshiba Satellite
http://forums.cnet.com/5208-12546_102-0.html?forumID=133&threadID=258491&messageID=2551857

Hope this helps.

Grif