I'd use NETINFO MANAGER in the Application/Utilities folder. Go to DOMAIN at the top (I think that's what it's called) and SECURITY. There is an option to AUTHENTICATE. Do this to allow you to change settings. Then go back to SECURITY and say ENABLE ROOT.
Follow the instructions. Log out, log in as root with the password.
When you're done. Log out, log back in as yourself -- go back to the NETINFO MANAGER and DISABLE ROOT.
Although the EASIEST way is to use BBEDIT (available at versiontracker). There is a demo available -- might be worth the purchase -- it will let you edit/save ANY file to yourhearts content without having to go through the hassle of enabling/disabling root priveledges.