if (document.images) {
   img1On = new Image();  img1On.src = "images/block-bcrs-on.jpg"; 
   img2On = new Image();  img2On.src = "images/block-edpm-on.jpg";
   img3On = new Image();  img3On.src = "images/block-out-on.jpg";
   
   img1Off = new Image();  img1Off.src = "images/block-bcrs.jpg"; 
   img2Off = new Image();  img2Off.src = "images/block-edpm.jpg";
   img3Off = new Image();  img3Off.src = "images/block-out.jpg";
}

function imgOn(imgName)
{
   if (document.images) {

      document[imgName].src = eval(imgName + "On.src");       
   }
}

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