function mail_file( $to, $subject, $messagehtml, $from, $fileatt, $replyto="" ) {

		$ext = strrchr( $fileatt , '.');
		$fileatttype = "";
		if ($ext == ".doc") $fileatttype = "application/msword";
		if ($ext == ".jpg") $fileatttype = "image/jpeg";
		if ($ext == ".gif") $fileatttype = "image/gif";
		if ($ext == ".pdf") $fileatttype = "application/x-pdf";
		if ($fileatttype=="") $fileatttype = "application/octet-stream";
		
		$file = fopen($fileatt, "rb");
		$data = fread($file,  filesize( $fileatt ) );
		fclose($file);

		$content = chunk_split(base64_encode($data));
		$uid = md5(uniqid(time()));

		$headers = "From: $from
";
		if ($replyto) $headers .= "Reply-To: ".$replyto."
";
		$headers .= "MIME-Version: 1.0
";
		$headers .= "Content-Type: multipart/mixed; boundary=\"".$uid."\"

";
		$headers .= "This is a multi-part message in MIME format.
";
		$headers .= "--".$uid."
";
		$headers .= "Content-type:text/html; charset=iso-8859-1
";
		$headers .= "Content-Transfer-Encoding: 7bit

";
		$headers .= $messagehtml."

";
		$headers .= "--".$uid."
";
		$headers .= "Content-Type: ".$fileatttype."; name=\"".basename($fileatt)."\"
";
		$headers .= "Content-Transfer-Encoding: base64
";
		$headers .= "Content-Disposition: attachment; filename=\"".basename($fileatt)."\"

";
		$headers .= $content."

";
		$headers .= "--".$uid."--";

		return mail( $to, $subject, strip_tags($messagehtml), str_replace("
","\n",$headers) ) ;

	}

function mail_file( $to, $subject, $messagehtml, $from, $fileatt, $replyto="" ) {

		$ext = strrchr( $fileatt , '.');
		$fileatttype = "";
		if ($ext == ".doc") $fileatttype = "application/msword";
		if ($ext == ".jpg") $fileatttype = "image/jpeg";
		if ($ext == ".gif") $fileatttype = "image/gif";
		if ($ext == ".pdf") $fileatttype = "application/x-pdf";
		if ($fileatttype=="") $fileatttype = "application/octet-stream";
		
		$file = fopen($fileatt, "rb");
		$data = fread($file,  filesize( $fileatt ) );
		fclose($file);

		$content = chunk_split(base64_encode($data));
		$uid = md5(uniqid(time()));

		$headers = "From: $from
";
		if ($replyto) $headers .= "Reply-To: ".$replyto."
";
		$headers .= "MIME-Version: 1.0
";
		$headers .= "Content-Type: multipart/mixed; boundary=\"".$uid."\"

";
		$headers .= "This is a multi-part message in MIME format.
";
		$headers .= "--".$uid."
";
		$headers .= "Content-type:text/html; charset=iso-8859-1
";
		$headers .= "Content-Transfer-Encoding: 7bit

";
		$headers .= $messagehtml."

";
		$headers .= "--".$uid."
";
		$headers .= "Content-Type: ".$fileatttype."; name=\"".basename($fileatt)."\"
"; // use different content types here
		$headers .= "Content-Transfer-Encoding: base64
";
		$headers .= "Content-Disposition: attachment; filename=\"".basename($fileatt)."\"

";
		$headers .= $content."

";
		$headers .= "--".$uid."--";

		return mail( $to, $subject, strip_tags($messagehtml), str_replace("
","\n",$headers) ) ;

	}

http://www.barattalo.it/2010/01/10/sending-emails-with-attachment-and-html-with-php/

Function to send HTML emails with an attachment in PHP. Notes and info at the above url!

Sending emails with attachment and HTML with PHP

PHP