(But it does not say anything about PimPamPet's Patch (nice play of words, isn't it?), so I guess he's wrong
and there really is no existing fix to the mouseproblem under Windows 2000 or XP.)
No idea; but if he says he has it, he could easily post it on his site, rapidshare, or somesuch. I have never encountered such a patch myself. Do share if you get ahold of it.
I do know some releases of Doom95 were missing mouse.vxd, and one needed to add it to make the mouse work, but on Windows 9x.