if (document.images)
   {
     pic1on= new Image(15,18);
     pic1on.src="images/overknop-home.gif";  
     pic2on= new Image(117,40);
     pic2on.src="images/overknop-over_concorp.gif"; 
     pic3on= new Image(117,40);
     pic3on.src="images/overknop-merken.gif"; 
     pic4on= new Image(117,40);
     pic4on.src="images/overknop-vacatures.gif"; 
     pic5on= new Image(118,40);
     pic5on.src="images/overknop-contact.gif"; 

     pic1off= new Image(15,18);
     pic1off.src="images/knop-home.gif";
     pic2off= new Image(117,40);
     pic2off.src="images/knop-over_concorp.gif";
     pic3off= new Image(117,40);
     pic3off.src="images/knop-merken.gif";
     pic4off= new Image(117,40);
     pic4off.src="images/knop-vacatures.gif";
     pic5off= new Image(118,40);
     pic5off.src="images/knop-contact.gif";

   }

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;
    }
 }