Changing User ID

Due to staff changes,the User id on Win2000 PC’s need changing, however, I do not want the actual files,existing email, desktop, programs etc etc to change. I tried changing a user ID in Properties of the current user and lost the login for that user and got “new” user settings. Consequently all that was there before, is now not available…although the files appear to still be there under Docs & Settings. Is there a way I can just simply change a user name on a PC but keep everything as is for the next user?