I fixed it myself.
If you want to do it too, open ih_wp2punbb.php

Find:
$message = ih_cleanArticle($message);
Replace with:
//$message = ih_cleanArticle($message);

Anyone how how to make it post the complete post, including html? For some reason it is not posting the HTML into the punbb forum.

Thanks.

I did a little mod to this mod, I hope you don't mind frank. I have set it so that if it is an image file to just show the image in the post.

Just open viewtopic.php and look for (around line 332.:

$attach_output .= '<br />'."\n\t\t\t\t\t\t".attach_icon($attachment_extension).' <a href="./attachment.php?item='.$attachment_id.'">'.$attachment_filename.'</a>, '.$lang_attach['Size:'].' '.number_format($attachment_size).' '.$lang_attach['bytes'].', '.$lang_attach['Downloads:'].' '.number_format($attachment_downloads);

and replace that with:

                if ($attachment_extension=='jpg' || $attachment_extension=='jpeg' || $attachment_extension=='gif' || $attachment_extension=='png') {
                    $attach_output .= '<br />'."\n\t\t\t\t\t\t".'<a href="./attachment.php?item='.$attachment_id.'"><img src="./attachment.php?item='.$attachment_id.'&download=1" border="0"></a><br>'.$attachment_filename.', '.$lang_attach['Size:'].' '.number_format($attachment_size).' '.$lang_attach['bytes'].', '.$lang_attach['Downloads:'].' '.number_format($attachment_downloads);
                } else {
                    $attach_output .= '<br />'."\n\t\t\t\t\t\t".attach_icon($attachment_extension).' <a href="./attachment.php?item='.$attachment_id.'">'.$attachment_filename.'</a>, '.$lang_attach['Size:'].' '.number_format($attachment_size).' '.$lang_attach['bytes'].', '.$lang_attach['Downloads:'].' '.number_format($attachment_downloads);
                }

Maybe someone can modify it some more to create a thumbnail using GD.