Windows

Are you sure that it cause by downloading the Win-XP image from the RIS server?

Track down that error in the Event Viewer or AD User and Computer and see why your local administrator account is disable.

Many times images are created with an account called Administrator that are then disabled. The actual built in adminitstrator account is renamed to something else. Find what it was renamed to first.
The actual built in administrator account cannot be disabled, but it can be corrupted, in which you will need to replace the account. (check out www.sysinternals.com and find ERD COMMANDER). This isnt the only tool for the job, but it works well.