Accessing the root account is disabled by default in Snow Leopard. Luckily enabling it is pretty simple and takes less than 2 minutes.
Warning: Enabling the root account can leave your Mac vulnerable to security threats. Only enable it if you are aware of the risks and know what you are doing.
. Open the Directory Utility located in /System/Library/CoreServices/.
. Unlock the application by clicking the padlock icon and entering your Administrator login.
. From the Edit menu, select Enable Root User.
. Chose Change Root Password from the Edit menu and chose a password for the root user.