function addLoadEvent(func) {
	var oldonload = window.onload;
	if (typeof window.onload != 'function') {
		window.onload = func;
	} else {
		window.onload = function() {
		  if (oldonload) {
			oldonload();
		  }
		  func();
		}
	}
}

function internalNav() {
	var nav = document.getElementById("leftNav");
	if (!nav) return false;
	var links = nav.getElementsByTagName("a");
	var wrapper = document.getElementById("mainContent");
	var divs = wrapper.getElementsByTagName("div");
	for (var i=0; i<divs.length; i++) {
		divs[i].style.display = "none";
	}
	for (var j=0; j<links.length; j++) {
		links[j].onclick = function() {
			for (var k=0; k<divs.length; k++) {
				divs[k].style.display = "none";
			}
			var elem = document.getElementById(this.getAttribute("href").split("#")[1])
			elem.style.display = "";
			return false;
		}
	}
}

addLoadEvent(internalNav);