Microsoft wants to sell XP Pro for twice the price in the corps, and since the corps all have domains, they made it imposible for Home to join a domain.
Not a lot of difference otherwise it seems, at least according to the XP Pro magazines they've been binding into the trade rags.
Next thing you know they will limit the TCP/IP connections to just 15 concurrent ones so XP Home won't be used as a web server. :)
"In order to completely solve a problem, you must make sure that the root of the problem is completely removed! If you leave the root, the problem will come back later to get you." - Norman King