AD 2003 need to add Domain user Group to local admin group on windows xp

I have a windows 2003 Domain and would like to add a sub admin group and add them to the local Administrators group on my windows xp workstations. Plus, create a power users group and add them to the local Power users group on the workstations. One way I’ve done it is through login scrip and using “net local group”. But, the login script only works if an Administrator logs in and runs it. I would like to use GPO to do this. Such as the default behavior of Domain Admins group is automatically added to the local administrators group.