Allow NT users to install programs

I am attempting to have users install & upgrade antivirus software via login scripts.

This requires that all users are allowed to install programs (ie update registry).

How can I relax this restriction in NT?

I have checked in User Rights, and Policy Editor but nothing jumps out at me.
As we have a mixed group of users I do not want to enforce programs that can be run in Policy Editor.

Thanks in advance,
AlanB