It is easy to reset your password just by popping in the OS X CD that came with your computer and reset the password. Same as easy if that CD is not around as well.
Here is how to reset your OS X password without an OS X CD. You need to enter terminal and create a new admin account:
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