I suggest to use Swiftmailer. It is up to date, easy to install and use. You can install it via PEAR, but there are lots of other options you might find more convenient as well.
Example code to send a mail with an attachement taken from the manual:
require_once 'lib/swift_required.php';
// Create the message
$message = Swift_Message::newInstance()
// Give the message a subject
->setSubject('Your subject')
// Set the From address with an associative array
->setFrom(array('john@doe.com' => 'John Doe'))
// Set the To addresses with an associative array
->setTo(array('receiver@domain.org', 'other@domain.org' => 'A name'))
// Give it a body
->setBody('Here is the message itself')
// And optionally an alternative body
->addPart('<q>Here is the message itself</q>', 'text/html')
// Optionally add any attachments
->attach(Swift_Attachment::fromPath('my-document.pdf'));