mac address auth question

Hi, i'm using freeradius 1.0.5. i make a pppoe server with rp-pppoe and freeradius without mysql and i make auth by username and password all i need to add to my configuration a check if mac address and if valid accept ( a mac address authentication but without mysql ) so how can i make this think and thanks in advanced . Sorry for my bad inglish --------------------------------- Yahoo! Music Unlimited - Access over 1 million songs. Try it free.