Admin Account does not have Admin Privileges

Here's the story
iMac 20" Aluminium
One of twenty for a school lab
Customised one from scratch, fresh OS install from accompanying disk set, installed all applications, ran all updates for OS and all applications, repaired permissions before and after.
Admin account in place, obviously.
I log in as admin and can open most applications. I cannot, however, open System Preferences.
I am told "Admin does not have permission etc". I did not set up a root account, and didn't really want to at this stage as it has not been necessary before.

Anyway, as access to System Preferences was not possible, I started up the iMac in target mode and booted my Mac Mini from the iMac OS. I could then log in as admin and access System Preferences.
In Accounts I created a second account which I called Admin1, and gave it admin privileges.

I repaired Permissions (twice) again. Disk Utility worked under this Mac Mini log in, but did not work when logged in directly on the iMac.

I logged out, shut down, detached the firewire cable and started up the iMac. It allowed me to log in using the new Admin1 account, but I still cannot access System Preferences. It is not connected to a network, as I have experienced Admin issues in the past when servers seem to interrupt some processes, because they have an Admin account too, of course.

I really do not want to go through the process of installing dozens of applications again (it's for an art lab, so has everything, with a full install taking six hours).

Has anyone experienced this weirdness and, more importantly, figured out a way to fix the problem.
I have been so careful with this configuration and have no idea what could have happened.

iMac details
2GHz Intel Core 2 Duo
2 GB 667Mhz DDR2 SDRAM

I cannot even open the More Info part of "About this Mac"..

I'm stumped. Help...

Thanks in Advance


Tony