Secpol (Score 1)

Every one of the XP workstations should have a local security policy on it. Try Start->Run->Secpol.msc and change the setting so that the only users who have ability to install is the administrator. Change the administrator's name to something only you know and give it a 10 character password with 4 of those being non alpha minumum. Secpol will have the required settings you need.