Mail question

I have a quick, probably easy to answer question. I am trying to add the ability to email from like a quest book or a calendar event and get an authentication error in my error log. I can only believe that this is due to my smtp server needed to know my login and password. Is there a way I can pass this in the php.ini file? I am using apache 2.0 and PHP 4.03 on a windows xp machine. If this can be done, please let me know, any other suggestions would be welcomed. Thanks -Rich