1. Open NetInfo Manager (in /Applications/Utilities).Last I used it, that's how it was done. Not recommended for ordinary users, just developers and admins in Apple shops. Much of the security and stability problems in Windows is because people run as admin all the time. Running as root also enables the 'su' for root, one of the worst known security issues on any Unix-like OS so you should disable it again once you're done with it.
2. Select menu: Domain...Security...Authenticate
3. Enter the password for the account you're in right now.
4. Select menu: Domain...Security...Enable Root
5. You will be prompted to create a password for root.
Thanks. I cannot abide the control-freakishness of the front end, which means I can't use it as a home PC. At work, however, I'm looking to customize a computer to do just one operation, from command-line, and yet still getting standardization in hardware, so this might be the ticket.