OK... then you do.
I think you can:
1) Add the file field to the form using DW
2) Open your universal email server behavior and go to the attachments tab and add:
<?php echo($_FILES["{FileFieldName}"]["tmp_name"]); ?>
That should work, but it won't maintain the file name... you might try:
<?php echo($_FILES[$fieldName]["name"]."|WA|".$_FILES["{FileFieldName}"]["tmp_name"]); ?>
That could work to maintain the original file name in the email as well.