Domain Issue

I just moved an office from one building to another, and then added several computers to the network. The Server is 2003, workstations all XP Pro. All computers came up fine on the Domain except for one. I’ve struggled with this one for hours, and can’t get it to join the domain.
Simply, on Windows 2003, I add the user, then the computer to the AD, then at the Desktop PC, change the name of the computer, reboot, then change the workgroup to the domain, reboot, but then I won’t let the user join the domain after the reboot. Checked back on 2003 to make sure the user wasn’t locked out, reset the account, password, but can’t get this one to join the domain. Any help?? Thanks.