Change admin password on domain with restricted access (WXP-Pro)

[Bilsta]

For some strange reason i am able to change the local administrator password on a machine thats on a domain (at college) from a user account which is very limited by using the 'net user' command (net user adminitrator 12345) in command prompt, it only works on various machines not all! could someone please tell how to fix this and what causes it?

thanks