I Cannot grand administrative rights to new users in w2k3 Domain

Hi there ! i am system administrator in a firm i installed new domain controller and migrated all the users from old one just via exchange migration tool, my domain is w2k3 standard server and Exchange 2003 enterprise edition is installed on it. first time when i made my user account and given admin rights its working but afterwords when ever i try to grand any one its showing that a person is admin but when i check on XP client or Vista its a normal user which can’t install anything cant do much .. Please advise ….