Are you running out of disk space someplace?
And I'd check the XP home thing, as it's definitely NOT the same as XP Pro. It would be on the first disk in a readme under 'supported platforms' or similar, except that I'm not even sure if IMS9 was out when XP launched, but take a look.
BTW, Win2k sp3 also works fine for IMS9, though you do need to be careful if you've got any funky networking (or no networking), as the license ties to your network adapter...