On DevShed today, there's a new tutorial that seeks to show you how to create a MIME mailer class in PHP.
This article outlines the design of a PHP class for sending email with attachments. Everything you need to do this is supplied by the core PHP system, so nothing additional (such as non-bundled extensions) should be needed save for the required set up and connection between PHP and a SMTP mail package such as Sendmail or Postfix.
For details on setting up Sendmail and PHP, read through the appropriate section of the PHP manual. If you are already using the mail() function in PHP, you are ready to go right now.
They start off simple, creating the basic framework of the mailer class - to, from, subject, etc. From there, they build the header creation function to input the right information. Then, it's on to the heart of the matter - the "add attachment" function, and the "determine mime type" function". From there, the rest is simple...