function show_product_tab(tab_id) {

    var img_product = document.getElementById('img_product');
    var img_examples = document.getElementById('img_examples');
    var img_templates = document.getElementById('img_templates');
    var img_mailing = document.getElementById('img_mailing');

    img_product.src = "../images/button_set_01_r.png";
    img_examples.src = "../images/button_set_02_r.png";
    img_templates.src = "../images/button_set_03_r.png";
    img_mailing.src = "../images/button_set_04_r.png";

    var tab_product = document.getElementById('tab_product');
    tab_product.style.display = "none";

    var tab_examples = document.getElementById('tab_examples');
    tab_examples.style.display = "none";

    var tab_templates = document.getElementById('tab_templates');
    tab_templates.style.display = "none";

    var tab_mailing = document.getElementById('tab_mailing');
    tab_mailing.style.display = "none";

    var tab = document.getElementById(tab_id);
    tab.style.display = "block";
    tab.style.visibility = "visible";
}