Depending on what level you have the UAC on, the following thread might help.
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=211965#Post211965

If that doesn't help, it's likely you will have to do with an admin script targeting each pc or using a Startup Script.

For the very reason you are asking, I had to split my login script up into both a startup script and logon script. I attack the admin things in the startup portion and the user settings in the logon.