I agree with the other comments, if you added more ram XP would work better, but.....
as your not going to do that, then I would recommend ME or 2000. Alot depends on what your going to use the PC for, as 2000 has all the security you could want, while ME, has all the multimedia support you could want.
by the way, www.techspot.com have a download page with ALL the updates you need for either. (saves time from going to windowsupdate site)
LIke all the others have said you need more ram. However in my experience Win2k is as hungry for ram has Win XP is. So if you are not going to get more ram you might want to go back to ME but who wants to go backwards. Just get some more ram and continue forward.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS