MySQL DB CleanUp Help!

Hello ! I'd like to automatically delete old entries from my MySQL .... Is there any special funcion in PHP or MySQl for doing that ? For that purpose, I've created a PHP script (form) that delete old entries when I submit a form ... but I'd like the scrip to do the job periodically(for instance once in two days or in a week) without my intervention... Is this possible ? ( I'ts on a UNIX server) Thanks.. Arcad.