You can use the command I mentioned on any workstation; I use it all the time, as long as the workstation is a member of the domain and you have admin rights, it will work.
You omitted the "/domain" switch though. This is what routes it from the local workstation to the domain controller.
If I use 'net user danomac /domain /active:no' on my workstation, it sends it to the domain controller and disables the account. If you omit the '/domain' the command will respond with 'User not found' or something like that (unless the user exists in the local userlist).
Daniel.