Automatic updates/SP2 problem

Hi,

I administer about 3000 (XP) machines and I have Automatic Windows update
installed on all of them. The service is set up in the "Download and install
at the specified time" mode and has always installed security updates with no
problem. The problem is that it will not install SP2 automatically, unless
the user is an admin on the machine and then they get a message in the
taskbar area stating that the SP is ready to install. Users who are not
local admins get nothing and nothing happens at the scheduled automatic
install time. Any ideas???