Being pedantic, I should point out that Office 2010 isn't actually compatible with Windows XP any more, as recent security updates include a version of MSO.DLL with isn't XP compatible.
It is therefore necessary to use an out of date version of MSO.DLL for the programs to run on XP, potentially opening up security risks.
Microsoft have shown no sign of addressing this problem, despite being told about it, so I can only assume that as far as they are concerned, XP compatibility has been dropped.
That's why I said "supposedly" in my post.