function checkform ()
{
 if (document.form1.email.value == "" || document.form1.email.value.indexOf ('@', 1) == -1 || document.form1.email.value.indexOf ('.', 3) == -1) {
   	alert( "Please enter a valid email address." );
   	form1.email.focus();
	return (false);
  } 
  if (document.form1.computer_id.value == "") {
    alert( "Please enter Computer ID." );
    form1.computer_id.focus();
    return false ;
  }
  if (document.form1.backurl.value == "") {
    alert( "Please enter Backlink URL." );
    form1.backurl.focus();
    return false ;
  }
  return true ;
}