function onTrack(track)
{
  imgSrc = '../img/' + track + '_on.jpg';
  imgName = 'headerNav_' + track;
  switchImage(imgSrc, imgName);
}
function offTrack(track)
{
  imgSrc = '../img/' + track + '.jpg';
  imgName = 'headerNav_' + track;
  switchImage(imgSrc, imgName);
}

function onUtility(utility)
{
  imgSrc = '../img/' + utility + '_on.gif';
  imgName = 'headerUtility_' + utility;
  switchImage(imgSrc, imgName);
}
function offUtility(utility)
{
  imgSrc = '../img/' + utility + '.gif';
  imgName = 'headerUtility_' + utility;
  switchImage(imgSrc, imgName);
}

/* handle the global nav hover effect */
function navchange(type,image_name,image_new_url){
  // type=0 (turn off) or 1 (turn on)
  // image_name is the name= parameter of the nav button in question
  // image_new_url is the URL of the new image to show for image_name
  if(!document.images) return;
  // if the image is currently active - that is, we are already ON the page in question - there is no effect
  if( document[image_name]&&document[image_name].src&&document[image_name].src.indexOf('_on.')>-1 ){
    return;
  }
  // if the instruction is to go back to normal (turn off) then that is easy:
  if(!type){ 
    MM_swapImgRestore();
    return;
  }
  // so the instruction must be to turn "on" the roll-over state
  MM_swapImage(image_name,'',image_new_url,1);
  
}