function updatePresenter() {
  if (document.forms[0].presenter.checked == true)
    displayOn('presenter_details');
  if (document.forms[0].presenter.checked == false)
    displayOff('presenter_details');
}

// FOLLOWING THREE FUNCTIONS FROM:
// http://www.uwex.edu/infosys/aws/repository/paste/38 

// the following to functions allow you to have precise
// control over the display
function displayOff(nr) {
  if (document.all)
    document.all[nr].style.display = 'none';
  else if (document.getElementById)
    document.getElementById(nr).style.display = 'none';
}

function displayOn(nr) {
  if (document.all)
    document.all[nr].style.display = 'block';
  else if (document.getElementById)
    document.getElementById(nr).style.display = 'block';
  }
  
// I DONT THINK I NEED THIS ONE
function displayToggle(nr) {
  if (document.all)
    document.all[nr].style.display = (document.all[nr].style.display == 'none') ? 'block' : 'none';
  else if (document.getElementById)
    document.getElementById(nr).style.display = (document.getElementById(nr).style.display == 'none') ? 'block' : 'none';
}