How to assign preffs to users not in a group?

Im sure this is easy.
I have a load of students starting term soon and there will not be enough time to move them all into groups before they start using the computers. What I want to do is anybody not in a group to be assign guest user privilages (ie very locked down) Then I can slowly move users into groups as they need accounts opening up.

I thought you do this using Guest Computers in WM, but when I select “define Guest Computers preffs here” although it seems to assign preffs to users not in a group, it seems to assign some preffs to users in groups!

For instance, I am in a admin group. I have selected our group to have teh dock on the left, and the guest users to have it on the bottom. Also the homepage is set to http://www.admin.com for admins and http://www.guest.com for the guests. Now very odly, if I log in as me, the preffs have been set rigfht for the dock, but safari points to http://www.guest.com! If I change guest computers back to inherit, when I logon, my homepage is http://www.admin.com.

Am I doing something wrong?
Oh and I should say that our accounts are Active Directory accounts managed in WM using the magic triangle.