windows server 2003 domain’s client can not install softwares

the user is logged-in with his username on our domain

let me clear that powerusers are not domain users , powerusers are workgroup users. and I don’t want to use UAC feature of vista. also I don’t want to make him member of Administrators group.
if anybody can tell me the steps so that I can touch server once to solve this problem for domain users.