if (document.images){
        pic_1_on = new Image();
        pic_1_on.src="img/nav_1_on.gif";
        pic_1_off = new Image();
        pic_1_off.src="img/nav_1.gif";

        pic_2_on = new Image();
        pic_2_on.src="img/nav_2_on.gif";
        pic_2_off = new Image();
        pic_2_off.src="img/nav_2.gif";

        pic_3_on = new Image();
        pic_3_on.src="img/nav_3_on.gif";
        pic_3_off = new Image();
        pic_3_off.src="img/nav_3.gif";

        pic_4_on = new Image();
        pic_4_on.src="img/nav_4_on.gif";
        pic_4_off = new Image();
        pic_4_off.src="img/nav_4.gif";

        pic_5_on = new Image();
        pic_5_on.src="img/nav_5_on.gif";
        pic_5_off = new Image();
        pic_5_off.src="img/nav_5.gif";
}

function imgOn (imgName){
  if(document.images){
        document['pic_'+imgName].src=eval("pic_" + imgName + "_on.src");
        }
}
function imgOff (imgName){
  if(document.images){
        document['pic_'+imgName].src=eval("pic_" + imgName +"_off.src");
        }
}