Unwanted local user in XP

Hi Y’all,
On the network I look after, a lot of PCs have been identified as having a user account that can be logged on to locally giving full admin access to the machine thus bypassing all security measures in place.
I can get rid of this by logging on to the machine as an administrator and deleting the admin rights from the user. This solves the problem but with 600 PCs on the newtork, can anyone point me at a quick solution/script etc that will do the biz?
Ta.