Network config

You disable access to control by not making the users administrators of the local system. If you use a GPO to make these setting changes, but they are local administrators, they can over-ride the security settings made by GPO.

I'd advise reading through the Group Policy Settings reference for XP SP2:
http://www.microsoft.com/downloads/details.aspx?FamilyID=ef3a35c0-19b9-4acc-b5be-9b7dab13108e&DisplayLang=en

Limiting the account to "power User" or just "user" will help, but you will get far more specific control of your end-users by the implementation of policies. Do a search on Microsft's website for "policies". Each part of the O/S (and every M/S application) has integral policy controls that limit/allow specific end-users as to availabilty, access and function.

MS just released a Technet article about using Group Policy to lock down Terminal Server sessions. Willing to bet it has everything you're looking for.

http://support.microsoft.com/default.aspx?scid=kb;en-us;278295

You need to stain your hands digging inside the windows registry, which takes forever to turn on/off, or there is a tool that graphically shows you what to display / disable etc.. and makes it easy.. check it out "system mechanic 4.0 "