[Moo] question about this object

[silent]

hi list,

I found this piece of code works different in IE6 and firefox3.5:

      function hook(el) {
//        var sub_id = $('sub_id'); // use this will ok in two browsers
          var sub_id = el; // if use this, next line will fail in IE6, but
works in firefox3.5

          var el2 = sub_id.getParent();
          alert(el2);
          return false;
      };
<input type="submit" id="sub_id" onclick="hook(this)" value="click"/>

though at last I find out use "var sub_id = $(el)" also work,
but could someone give me a describe on this problem ?

thanks!