You need to obtain the Resource Kit. In it is a the Remote Desktop Admin. You will run a very similar RDP (Remote Desktop Protocol) to do so.
if you are trying to assist users from a remote workstation, you can always, configure NetMeeting, then deny 1270 and 1503 ports at the firewall to prevent all traffic in / out to the world on the same software.
The user will have to launch and give you control, but can save you a lot of stairs if that's the case.