That's begging to be cracked. Now that i think about it, I've heard you turn XP Home into Professional in a way.
Microsoft plans to implement a way for users to upgrade their version of Windows Vista online. Have Vista Home Basic, and want Home Ultimate? No problem. Hit the Control Panel, and choose your upgrade. Details here:
http://www.internetweek.cmp.com/showArticle.jhtml?articleId=181401967
-Terry

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic