change local computer policy on windows 2003 terminal server

The terminal server time outs are a per-machine setting. There is no way you are going to be able to have a per-computer setting behave differently per user.

You can set per-user session limits via policy, but you cannot use a local policy. You'll have to setup a policy on your domain place it in an OU with your terminal server, set up loop-back processing, and set the per-user session limits. See (User Configuration\Administrative Templates\Windows Components\Terminal Services\Terminal Server\Session Time Limits)

Refs:

• http://technet.microsoft.com/en-us/library/cc754272(WS.10).aspx
• http://technet.microsoft.com/en-us/library/cc758177(WS.10).aspx