Which OS?
If you're under XP/2000, then getting to a command prompt and typing:
net localgroup administrators
will list all current administrators.
Typing:
net localgroup administrators %name% /del
Will remove %name% from the administrators group.
Now, if you need to reset the Administrator account's password, you can use either the user management tool, or you can use [link|http://home.eunet.no/~pnordahl/ntpasswd/|this] tool...
The most exciting phrase to hear in science, the one that heralds the most discoveries, is not "Eureka!" but "That's funny..."
-Isaac Asimov