I went from XP Home to XP Pro and haven't had any problems.
Actually I think there are only two issues with upgrading your current OS to XP:
1) Go with at least 256mb ram for XP and of course the required disk space for installation.
2) Be prepared for driver hunts. If you'd like to re-use any peripherals, network cards, etc currently attached to your pc make sure you have the drivers for XP before you upgrade.
It took me damn near a month to find XP drivers that work with a Voodoo 5 card plus I had to get a new printer because the manufacturer of my old printer wasn't releasing drivers for that old model on XP.
