change domain controller

hi
i`ve three server [one domain controller(192.168.1.1),one isa server(192.168.1.2)and one data server(192.168.1.3)]running windows 2003 and 20 clients running xp.i purchased new one pc with original windows 2003 server r2.so i need to change my domain controller to the new pc without problems.please help me….