If this be a Firmware Password that appears before startup, then they can try removing the battery, disconnecting the charger, removing all memory modules, wait one minute, then reinsert. Restart the computer. This may work.
If this is an account login password:
Forgot Your Account Password
For Snow Leopard and earlier with installer DVD
Mac OS X 10.6- If you forget your administrator password,
OS X- Changing or resetting an account password (Snow Leopard and earlier).
For Snow Leopard and earlier without installer DVD
How to reset your Mac OS X password without an installer disc | MacYourself
Reset OS X Password Without an OS X CD — Tech News and Analysis
How To Create A New Administrator Account - Hack Mac
Or boot from an installer disc and erase the drive completely.