Changing computer names on domain

[mathmatik]

I wanted to change the computer names on my network to something that is easier to keep track of and when I log into the admin profile on my domain and try and change the computer name I get an error saying either the credentials I used to changed the computer name is incoorect or it says its says its using the computer name thats already on the server. I got one od the computers using XP to change the pc name just by pressing enter a few time but this of course is inefficient. any help would be appreciated. Peace