function menu_change(tab)
  {
	// first clear links for the previous tab, by setting all to display: none
	document.getElementById('nav_tab_links_home').style.display = "none";
	document.getElementById('nav_tab_links_solutions').style.display = "none";
	document.getElementById('nav_tab_links_courses').style.display = "none";
	document.getElementById('nav_tab_links_schedules').style.display = "none";
	document.getElementById('nav_tab_links_success').style.display = "none";
	document.getElementById('nav_tab_links_instructors').style.display = "none";
	document.getElementById('nav_tab_links_events').style.display = "none";
	document.getElementById('nav_tab_links_resources').style.display = "none";
	document.getElementById('nav_tab_links_about').style.display = "none";

	// change the background image
	document.getElementById('nav_tab_menu').style.backgroundImage = "url('images/" + tab + "_menu.png')";

	// display the links for the new tab
	document.getElementById('nav_tab_links_' + tab).style.display = "block";

	return;
  }