How do I reset lost password

thats pretty easy, i'll quote apple on that matter:

"You don’t remember your password and need to reset it

If you don’t remember your password and you have the Mac OS X installation disc, insert the disc and restart your computer while holding down the C key. If your computer doesn’t have an optical drive, use Remote Install Mac OS X. When the Mac OS X Installer appears, select your language, choose Utilities > Reset Password, and then follow the onscreen instructions."

very short version, boot from your setup dvd, go to the utilities, reset the password and quit the setup