Some of the differences may have disappeared in SP2 but this is a pretty good list of the differences:
http://www.winsupersite.com/showcase...p_home_pro.asp
32-bit editions of XP Home and Pro (at least with SP2) use the same drivers.
Using XP Pro certainly won't hurt but most of the "extra" features aren't things most of us use anyway. The primary difference was always SMP support but XP Home at least with SP2 supports dual core CPUs now so unless you plan on going with a 2 socket motherboard and running a pair of them, there really isn't much to get worked up about.
Kuddos to Microsoft for working their marketing magic on Jelly Belly though :P
XP Pro x64 is indeed a different beast, however. It pretty much requires the same drivers as the x64 version of Windows Server 2003 and it usually somewhat behind.