Forgot my password
For got my password, how can I resit my password
If you're running OSX, you can boot to the system CD and look in the Utilites (or possibly another) menu for the password reset utility. Resetting this password will let you log on and install software, but without your original password, your keychain's stored passwords will be inaccessible (for email, etc.)
If you're running OS9 then it's the firmware password. Sorry, I can't remember if that can be bypassed or not.
Here's another article that may be helpful:
Take back to a store that specializes in your computer. They should be able to reset it.