Log on script

Hello guys. I need help in a very tricky situation, and any sugestions you may have would be very much appreciated.
I have a 250 computers network. I have AD, DHCP, DNS installed. I want to change the local administrator password (on each computer)but I don’t want to do that by going to each user place. I want to do that by using a script policy applied at the machine level. The problem is that I am not that good on scripting, and I wonder if you may help me with detailed sollutions to do that. I thank you a lot and waiting for your suggestions.