|a possible option|
You can put any OS X disk into the drive and reboot - right after the chimes, press and hold the C key to boot from the DVD. Select your language, and on the next screen click on Tools at the top of the screen, then Reset Password.
If you totally can't get your hands on an OS X disk, the Apple Store will let you borrow one for free, and they will re-issue the Restore Disks for a few bucks.
not the best choice