Active Directory Users Security Not Save

I have 3 DC. 2 running 2003 Server and 1 running 2000 Server. I am setup with Administrator permission. I login to one of the Win XP PC with the admin pack installed. I went to Active Directory Users and Computers and changed individual user’s security setting. Everything work the way it supposed to. But after an hour or 2, the changes I made were gone. I tried that on a PC, the 2003 DC, and the 2000 DC. It is the same. After an hour or 2, the changes will disappeared. How can I save my changes?