I used a freeware program called Registry cleaner (not MS's RegClean!) for
this with my Win98 PC and I see that the latest version works with Win2000.
I suspect it could be very useful for those many programs which I've
installed and, in spite of warnings about not having installed, are actually
working fine. But I bet the uninstaller won't work when I want to get rid of
them.
http://www.pcmedixwebs.com/regclean.htm
With some programs, my only choice was to delete the program's files from my
hard drive and then use reg cleaner to get rid of the registry entries and
orphaned dlls.
As it says on the page above though, always back up your registry first.
BTW there are some programs which get so wound into the PC's system that a
simple solution like the above would not work so as Rick says, tell us what
it is.
Evi