function ischecked(){
   if(document.add_link.action.value == "edit"){
      return true;
   }
   var checked=0;
   for(i=0; i<document.add_link.elements.length; i++)
   {
      if(document.add_link.elements[i].type=="checkbox"){
         if (document.add_link.elements[i].checked){ 
            checked = 1;
            break;
         }
      }
   }
   if(checked == 0){
      alert("You must check at least one URL.");
      return(false);
   }
   else{
      return(true);
   }
}

function checkall(value)
{
   for(i=0; i<document.add_link.elements.length; i++)
   {
      if(document.add_link.elements[i].type=="checkbox")
      {
         document.add_link.elements[i].checked=value;
      }
   }
}