function getHttpRes( ) {
  if (http.readyState == 4 && http.status == 200) { 
    res = http.responseText;
    $("#promo_table").html(res);
  }
}

function viewCat (var1, var2, var3){
       //process
       params = "cat_id=" + encodeURI(var1) + "&cat_type=" + encodeURI(var2) + "&page_num=" + encodeURI(var3);
       doHttpRequest("./ajax_promo_table.php");
}

function viewDetails (var1, var2, var3){
       //process
       params = "cat_id=" + encodeURI(var1) + "&item_id=" + encodeURI(var2) + "&page_num=" + encodeURI(var3);
       doHttpRequest("./ajax_details.php");
}