Downgrading Win 2000 Server to XP or …

I want to down grade a couple of systems
that running on Windows 2000 Server. I have
software that is on the systems that have
updates to the software and the company is
no longer around. If would like to try and reinstall on Win XP I don’t want to have to go to 2003 server. It never needed to be on a server platform in the first place. (big mistake) and Ideas???