I despise WinME. It's odd why you had such good luck with ME but I've seen others who have run WinME with no issues.
XP, i'm running Pro build 2600 on 3 systems now, all different configurations, it's nice.
A few things.
XP uses 80MB of ram for itself. I'd reccomend 256MB.
A 500MHz CPU seems to be the minimum. If your going to let it sit on a rack & run as a server a slower CPU will do. But if your going to be using a XP system on a regular basis be sure to be running better then 500MHz.
Game compatiblity is OK, not great. Games you would think would work, done. Yes you do have the option for compatiblity mode & it actually worked for Star Trek Elite Force.
If your hardware manufacture doesn't have a driver, get the Win2K driver.
Quickbooks 2000 works but the update barfs out on ActiveX, you never know what will & won't run with XP. But over all it's VERY stable, quick, & you MUST disable that POS "Luna" interface. Finding ANYTHING their this interface is a joke. Disable it.