Even if you did not enable the root user in NetInfo, it is very simple to become the root superuser with unlimited privileges. You need to have an admin account and start a Terminal session. In the Terminal, you type this:
% sudo suThen enter your own password and presto uid 0 is yours...
% id uid=0(root) gid=0(wheel) groups=0(wheel), 1(daemon), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest), 80(admin)[robg adds: I find it much safer to just use sudo followed by the specific command to be run; the above command sets you as the root user until you type exit. One little simple mistake (rm -rf ... in the wrong directory, for instance!), and you'll soon regret your all-encompassing root privileges. sudo some_command times out after a couple minutes, requiring your admin password again to activate the next time you run it.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031124042814764