password changing for windows users

Heres the situation, I have my windows users authenticating on my osx server using samba, they can change their passwords just fine using control-alt-del change password. Problem is, webmail users (remote users) have no way to change their passwords cause they dont log on to the local network, they only use webmail (squirrelmail). Can anybody point me in the right direction ? I want to have a password change page on my intranet, but i have no idea where to start, I can code in php (not really a noob, but not a uber programer either) but I get confused just thinking about this idea. Any pointers ? plzzzz ? :D TIA Fernando Battistella.