I've installed it on XP but had a few problems with it such as mouse rollover colours wrong, menu items showing wrong background colours and no matter what I could'nt get it right. I'm sure some users will report no problems but it does mess with system files.
It did uninstall OK but left desktop colours etc for me to put back as they were before, which was no big deal. Just be sure you make a restore point before installing it.
EDIT: I did use version 5 though