Enable Super User on Mac OS X 10.5 & 10.6

For whatever reason, Apple decided to bury the Directory Utility application in Snow Leopard. You will no longer find it in the utilities directory, but it still exists in /System/Library/CoreServices. Simply "Go" there by selecting "Go to Folder" from the Finder menu (⌘⇧G), and type the path into the field. From here on out, the process is the same for Mac OS X 10.5.

Launch Directory Utility (Found in /Applications/Utilities under OS X 10.5 & Earlier), click on the padlock to make changes and enter your administrator password. From the "Edit" menu, select "Enable Root User". You will have to enter a password (make it a good one!). The root, or super user is now available to users with administrator privileges.

One note about using "su" versus "sudo". Both of these terminal commands will prompt you for a password. When using "sudo", enter your user password. When using "su", enter the root password that you setup in the Directory Utility