THE administrator account? Or one that you see in normal mode with administrator privileges?
If it's the former, it shouldn't have a password, and it should be enabled by default. WinXP does this in case you forget your password or if a virus destroys your ability to log in. No need for a script.
If it's the latter, I suggest the DOS command: "net [user] [password]" without the quotes, replacing user with the name of the login, and replacing password with the chosen password.