Mail attachment problems

Can anyone out there work out why this code won't work with attachments? It'll post mail without attachments though.

Code:

$form = "
<form action="formmd.php" method="post" enctype="multipart/form-data">
<input type="hidden" name="seenform" value="y">
<b>Email the Committee</b><br><br>

<table border=0 align=center cellpadding=0 cellspacing=0 marginwidth=0 marginheight=0 width=100% bgcolor=#996699>

<tr>
<td valign=top width=15%>Your Name: </td>
<input type="hidden" name="name" value="$user[1] $user[3]">
<td valign=top>$user[1] $user[3]</td>
</tr>

<tr>
<td valign=top>Your Email: </td>
<input type="hidden" name="email" value="$login@wycliffe.co.uk">
<td valign=top>$login@wycliffe.co.uk</td>
</tr>

<tr>
<td valign=top>Subject: </td>
<td valign=top><input type="text" name="subject" size="50" maxlength="50" value="$subject"></td>
</tr>

<tr>
<td valign=top>Message: </td>
<td valign=top><textarea name="message" rows="10" cols="45"></textarea></td>
</tr>

<tr>
<td valign=top>Picture:</td>
<td valign=top><input type=file name="attachment"></td>
</tr>

<tr>
<td colspan=2><input type="submit" style="background-color:transparent" value="Go Mail!"></td>
</tr>

</table>
</form>";


if ($seenform != "y") :
print($form);
else:

// check for valid file if attachment exists
if ($attachment_name && $attachment_size <= 0)
{
echo "Bad Attachment<br>";
}

// build message headers
$headers = "From: $name <$email>";

// if attachments exist
if($attachment_name || sizeof($amsg) > 0)
{

// create a MIME boundary string
$boundary = "=_" . md5(uniqid(time())) . "_=";
echo "$boundary";

// add MIME data to the message headers
$headers .= "MIME-Version:1.0n";
$headers .= "Content-Type: multipart/mixed; tboundary="$boundary"nn";

// start building a MIME message
// first part is always the message body
// encode as 7-bit text
$str = "--" . $boundary . "n";
$str .= "Content-Type: text/plain;tcharset="us-ascii"n";
$str .= "Content-Transfer-Encoding: 7bitn";
$str .= "$messagenn";

// if an uploaded attachment exists
// encode it and attach it as a MIME-encoded section
if ($attachment_name)
{
$fp = fopen($attachment, "rb");
$data = fread($fp, filesize($attachment));
$data = chunk_split(base64_encode($data));
fclose($fp);

// add the MIME data
$str .= "--" . $boundary . "n";
$str .= "Content-Type: " . $attachment_type . ";tname="" . $attachment_name . ""n";
$str .= "Content-Transfer-Encoding: base64n";
$str .= "Content-Disposition: attachment; tfilename="" . $attachment_name . ""nn";
$str .= $data . "n";
}

// all done
// add the final MIME boundary
$str .= "n--$boundary--n";

// assign the contents of $str to $body
// note that the original contents of $body will be lost
$message = $str;
}

// send out the message
$to = "yb@wycliffe.co.uk";

echo "To: $to";
echo "Subject: $subject";
echo "Final Message: $message";
echo "Final Headers: $headers";

$mail = mail($to, $subject, $message, $headers);

if(mail($to, $subject, $message, $headers))
{
$status = "Your message was successfully sent.";
}
else
{
$status = "An error occurred while sending your message.";
}

echo "$status<br>";
echo "$mail<br>";

endif;


The variable $user is read from a MYSQL database.
The variable $login is passed by the script which accesses this one.
The script is called formmd.php and calls itself once the submit button is clicked.

Thanks,

John