Question : When trying to rename a machine on my windows 2003 domain it say's the user name could not be found.

I've tried to rename the netbios name of a computer in my school so that it's uniform with the rest of my computers. I go in change the name, and the login screen pops up asking for the username and password of a account that can rename the computer. I put the administrator account in, and it comes back. "The following error occured attempting to rename the computer to "???????": the user name could not be found. Please help. This is on a xp machine.

Answer : When trying to rename a machine on my windows 2003 domain it say's the user name could not be found.

Take it out of domain on PDC.
Reboot
Log on local to machine (not domain)
Change machine name.
Reboot.
Assign to domain.

One general rule is that you usually will have to reboot after each step for any cdhange to really take.  Another possibility is where you have more than one DC.  It can take perhaps about fifteen minutes for the network to stabilize on changes made.

>  the user name could not be found

This is the administrator for the domain, when adding to the domain.

You need to be local admin to change the name, but I do not recall that message as a part of that process