Want to spread your wings further? This article on Microsoft's TechNet site shows how you can assign a unique password to each machine.
On a Windows 2000 domain, you can also take advantage of a tool on the Windows 2000 Resource Kit CD to change administrator passwords without resorting to GPOs. Console User Manager (Cusrmgr.exe) enables editing of many of the Local Users and Groups user properties, including administrator passwords, from the command line.
Create a batch file, with one line for each machine whose password you need to change. For example, the following lines in a .bat file will change the local administrator password to newpass on the computers named \\pc1, \\pc2, and \\pc3:
cusrmgr.exe -u Administrator -m \\pc1 -P newpass cusrmgr.exe -u Administrator -m \\pc2 -P newpass cusrmgr.exe -u Administrator -m \\pc3 -P newpass
To run this batch file successfully, the user ID from which you're running it must have administrative privileges on the destination PCs. Also, note that you must use a capital P for the -P switch; a lowercase p sets the account password to a random string.
This method involves more effort, and may not be as successful as a group policy. A GPO is applied every time a domain machine starts up, so if the machine doesn't happen to be in use when you create the policy, it is still affected. The above batch file assumes the machines are available when it is run.
If none of these methods appeal, a Web search will find a number of scripts, developed by administrators, to do the job for you. Be careful, though, to test them thoroughly before turning them loose on your domain.