I need help creating a php mail form, I need to be able to send an attachment.?

[Kitty Juice]

Here is what I have so far (which works fine):
<?php
$to = $_POST['to'];
$from = $_POST['from'];
$sub = $_POST['sub'];
$msg = $_POST['msg'];
$headers = "From: ".$from. "\r\n";
$subject = "$sub";
$msg = "$msg";
if (mail($to, $subject, $msg, $headers)) {
echo("<p>Message successfully sent!</p>");
} else {
echo("<p>Message delivery failed...</p>");
}
?>
Now i just need to create something where there is a slot for an attachment. Tell me what I need to insert into the php.
(also what input type to add to my form in HTML)
-THANKS!