1. Reboot
2. Hold apple + s down after you hear the chime.
3. When you get text prompt enter in these terminal commands to create a brand new admin account (hitting return after each line):
   • mount -uw /
   • rm /var/db/.AppleSetupDone
   • shutdown -h now
4. After rebooting you should have a brand new admin account. When you login as the new admin you can simply delete the old one and you’re good to go again!

Thanks too..

http://theappleblog.com/2008/06/22/reset-os-x-password-without-an-os-x-cd/

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