We do this through Group Policy.
I don't know the specifics of how the GPO is created, but it is in the section:
Computer Configuration
/ Windows Settings
/ Security Settings
/ Local Policies/Security Options
/ Accounts
There are settings to allow disabling of the guest account and renaming of the local admin account.
EDIT: I misspoke about changing the local password.
Changing the local admin password is a bit more complicated, at least until Windows Server 2008. This solution works on Server 2003, and is a bit of a kludge as it sends the new password in plain text. If that concerns you, there are other alternatives that encrypt but need additional software. We address the issue by leaving it disabled unless we need to make a change.
1- write a 1 line batch file .. with the command "NET USER Administrator %1" - if you rename the account use the new name.
2- set the batch file to run on logon using the GPO, in the following section
Computer Configuration
/ Windows Settings
/ Scripts
/ Startup
3- IN THE GPO entry, press the button to show the files, and copy the batch file into the location opened. Then the batch file (incl .bat) as the script name and the new password as the parameter.