Out of free disk space

We are operating in an NT environment. My users are quickly running out of free space on their c:\, yet they have 1GB on D:\. What folders/applic. can I move over to D:\ and what folders/applic. should I not move? I also have a computer (NT) thathas WinNT running over top of Win95, how can I remove Win95 option?
Thank you!