Local Security Policy Issue

I have a set of questions for any one out there who can answer it. My first question is I have a user who is able to change his local permission profile on his pc from a user to administrator and I don’t know how he is doing this. By the way we are using Windows 2000 Pro. The second question if he is able to change his permission can he prevent us from accessing his pc )logging in and accessing any important data on it. The second question is.., if he is able to change his permission from user to administrator on his pc is there any way he could change his network profile from a user to administrator as well?

Thanks,

Jose Ferrer
jferrer@sacfirmonline.com