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

// prepare the walkthrough link so that it opens the walkthrough in a new, sized window
function prepareWalkthrough() {
	var walkthroughLink = document.getElementById('walkthroughlink');
	
	if (walkthroughLink != null) {		
		walkthroughLink.onclick = function() {
            var newWindow = window.open(walkthroughLink.href, walkthroughLink.id, 'height=480,width=640,resizable=yes');
			newWindow.focus();
            return false; // prevents default action
        }
	}
	
	return true;
}

addLoadHandler(prepareWalkthrough);