if (document.images)
   {
     pic1on= new Image(100,25);
     pic1on.src="nav_portfolio_over.jpg";  

     pic1off= new Image(100,25);
     pic1off.src="nav_portfolio_up.jpg";
   
     pic2on= new Image(100,25);
     pic2on.src="nav_resume_over.jpg";  

     pic2off= new Image(100,25);
     pic2off.src="nav_resume_up.jpg";
   
     pic4on= new Image(100,25);
     pic4on.src="nav_contact_over.jpg";  

     pic4off= new Image(100,25);
     pic4off.src="nav_contact_up.jpg";
   
        }

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;
    }
 }