ok, I can think of a few ways to do it...
you could install some kind of telnet server on their machine, then you'd have complete control to run or kil programs,
or you could try this... (only work for NT based computers)
net use z: \\[Computername]\c$ to browse to their C drive.
you might have to specify a username and password to connect, this should be thier username an password, or the administrator of that machine...
It's worth knowing that in windows XP if you are on a workgroups and you happen to have the same username and password on two computers, they have a password excahnge policy that automatically allows you to browse files on that machine as well...