This a walk through of how to add a Windows XP Professional client computer to a Windows 2003 Domain. Windows XP Professional is a requirement because Windows XP Home does not support this feature.
Start --> Settings --> Control Panel --> Launch the Systems applet --> Select the Computer Name tab --> select the Name button. The Computer Name Changes window will launch.
Select the Domain radio button then enter the name of the domain and click on Ok.
You will then be prompted to enter account credentials with rights to add a computer to the domain, do so. The computer is now added to the domain but may not be able to access the domain until Active Directory has replicated.
If you need to force Active Directory replication, start the Active Directory Sites and Services snapin. Then drill down to Sites --> Default-First-Site-Name --> Servers --> Server with the client computer object --> NTDS Settings. Then right click on the NTDS object and select replicate now. Keep in mind that the you pulling the Active Directory information from a server that contains the computer object to one that does not.