And the hack described below didn’t work with my new 10.3.3 version… This is how I did it. Start up your mac. Go to Applications / Utillities and open a Terminal.
Now type: 

sudo sh

Now give your (own) administrato password.
Now you should have a root shell.
Now type: 

passwd root

Now it’s asking for your new root password twice. Now press CTRL - D to exit the shell… Try your new root passw with the ’su’ command… Easy ;)