function switchDiv(div_id)
{
  var style_sheet = getStyleObject(div_id);
  if (style_sheet)
  {
    hideAll();
    changeObjectDisplay(div_id,"inline");
  }
  else 
  {
    alert("sorry, this only works in browsers that do Dynamic HTML");
  }
}

// function hideAll()
//  hides a bunch of divs
//
function hideAll()
{
   changeObjectDisplay("werk","none");
   changeObjectDisplay("studie","none");
}

// function getStyleObject(string) -> returns style object
//  given a string containing the id of an object
//  the function returns the stylesheet of that object
//  or false if it can't find a stylesheet.  Handles
//  cross-browser compatibility issues.
//
function getStyleObject(objectId) {
  // checkW3C DOM, then MSIE 4, then NN 4.
  //
  if(document.getElementById && document.getElementById(objectId)) {
	return document.getElementById(objectId).style;
   }
   else if (document.all && document.all(objectId)) {  
	return document.all(objectId).style;
   } 
   else if (document.layers && document.layers[objectId]) { 
	return document.layers[objectId];
   } else {
	return false;
   }
}

function changeObjectVisibility(objectId, newVisibility) {
    // first get a reference to the cross-browser style object 
    // and make sure the object exists
    var styleObject = getStyleObject(objectId);
    if(styleObject) {
	styleObject.visibility = newVisibility;
	return true;
    } else {
	// we couldn't find the object, so we can't change its visibility
	return false;
    }
}

function changeObjectDisplay(objectId, newDisplay) {
    // first get a reference to the cross-browser style object
    // and make sure the object exists
    var styleObject = getStyleObject(objectId);
    if(styleObject) {
	styleObject.display = newDisplay;
	return true;
    } else {
	// we couldn't find the object, so we can't change its visibility
	return false;
    }
}