Without the remote user knowing? No. There are applications but they are hacking tools for the most part.
You can use things like Netnanny and the Vista OS to limit peoples use of the Internet and monitor what they are doing - but you have to be an administrator and be local in order to load the application.
In terms of remote access again nothing you can use without the user knowing (if you find them they are hacking tools), but i would suggest Microsofts remote desktop utility, or logmein. Again both tools the user has to give you permission.