if (document.images)
   {
     pic1on= new Image(107,40);
     pic1on.src="images/overknop-prijzen.png";  
     pic2on= new Image(92,40);
     pic2on.src="images/overknop-route.png"; 
     pic3on= new Image(237,40);
     pic3on.src="images/overknop-reserveren.png"; 

     pic1off= new Image(107,40);
     pic1off.src="images/knop-prijzen.png";
     pic2off= new Image(92,40);
     pic2off.src="images/knop-route.png";
     pic3off= new Image(237,40);
     pic3off.src="images/knop-reserveren.png";
   }

function lightup(imgName)
 {
   if (document.images)
    {
      imgOn=eval(imgName + "on.src");
      document[imgName].src= imgOn;
    }
 }

function turnoff(imgName)
 {
   if (document.images)
    {
      imgOff=eval(imgName + "off.src");
      document[imgName].src= imgOff;
    }
 }