The solution I use is VNC ( http://www.uk.research.att.com/vnc )
This is an open source / cross platform remote desktop tool. Basically it ships the screen pixels back from a remote server to a local client, and forwards mouse and keyboard commands the opposite way. Not only can you run any program on the remote computer you can also watch what someone is doing - invaluable for help desks tracking user problems. Both the server daemon and client browser are available for windows + unix. Martin Beckett