Hi,

tge original code had some more backslashes
$html = preg_replace('/"CID(\d+)"/e', '$this->gen_id(\'\\1\')', $html);
maybe boldfacing prevents their removal

To attach a file, you could use
$files = array(
array(file => 'xy.jpg', mime => 'image/jpeg'),
array(data => $myswf, name => 'generated.swf', mime => 'application/x-shockwave-flash')
);
This code was originally developed to create e-card swf on the fly and email it, so the swf would exists as a string. If you read data from mail server, you will more likely have them as strings within memory than as disk files.
The CID mimikry is meant for images etc. inside a html message

Musicman