switch of userrights witout logout

Hi,

Does anyone know of a program that enable me to switch user rights witout logging out of the machine and logging in with the admin account?
Users use a GPRS connection to the office, after having problems we want to take control of the machine using VNC witch is installed under the user account. We maybe need to start installation of program’s but don’t want the user to have acces to those same programs and even have installation rights.

regards, Paul