function checkbox_set(obj, chk_name, img_prefix) {
    document.getElementById(chk_name).checked = !document.getElementById(chk_name).checked;
    img_src = img_prefix + document.getElementById(chk_name).checked + '.gif';
    obj.src = img_src;    
  }
  
  function set_description_text(obj, text, set) {
    if(set) {
      if(obj.value == '') 
        obj.value = text;
    }
    else {
      if(obj.value == text) {
        obj.value = '';
      }
    }
  
  }