The method below describes how to to access any Mac if you don't know the password.Locate that Mac’s installer disc or a recent OS X installer disc (a Tiger or Leopard disc, for example). Insert that disc into the Mac’s media drive and hold down the keyboard’s C key to boot the Mac from that disc.
When the Mac boots you’ll be asked to choose a language. Do that and click the right-pointing arrow icon to continue. When the Welcome screen appears wait for the menubar to materialize and choose Reset Password from the Utilities menu. In the resulting window choose the user whose password you want to change from the Select a User pop-up menu. Enter and confirm a password in the appropriate fields and, if you like, enter a hint for the password. Click Save to make the change.
Note that when you’ve reset the Administrator’s password you haven’t reset the login keychain password—that password remains as it was when it was originally set. What this means is that you’ll be able to do all the things an Administrator can—install applications and muck with all the Mac’s system preferences, for example. You can’t, however, access keychain items (web site passwords, for example) saved in that login keychain without the password originally used.
[via macworld]
