Are you wanting to do this remotely on multiple machines?
And doing a:
pspasswd @computers.txt -u <DOMAIN\Administrator> -p <domain admin password> administrator <new local admin password>
Doesn't work for you?
Okay maybe I don't understand... why would you want to do this on every startup?
Run the command I gave you with a file called "computers.txt" (with each computer name on a separate line in the file) and it will automatically run itself over and over again for each computer. No need for a script.