I'm going to take this opportunity to once again plug TqcRunas 2002.2 Edition.

This wonderful application is scriptable from the commandline and COM as well. I just used it to push out Service Pack 4 and the MS03-026 patches to our users who did not have admin rights on their workstations.

While it isn't free, it is very affordable (from 80 € for 10 seats to 3000 € for an Enterprise license).

It is secure as TqcRunas can read its command line from a strongly encrypted file. Therefore, you can exactly specify which programs and options your users can run with administrator's privileges without revealing the administrator's password.