Disabling Submit Button After Submission

[FatalBreeze]

Hello, I'm using this script to disable submit button after submission:

 function disableForm(theform) {
  if (document.all || document.getElementById)
  {
   for (i = 0; i < theform.length; i++)
   {
    var tempobj = theform.elements[i];
    if (tempobj.type.toLowerCase() == "submit" || tempobj.type.toLowerCase() == "reset")
     tempobj.disabled = true;
   }
   setTimeout('alert("Your form has been submitted.  Notice how the submit and reset buttons were disabled upon submission.")', 20);
   return false;
  }
 }

and everything works fine, but when i wrap the input elements with <fieldset> it just doesn't work.

Does anyone have a solution?

Thanks in advance.