if (document.images) {            
       img1on = new Image();   img1on.src = "images/folderhomef.gif";
	    img2on = new Image();   img2on.src = "images/folderboat3f.gif";
	    img3on = new Image();   img3on.src = "images/folderbooking3f.gif"; 

       img1off = new Image();  img1off.src = "images/folderhome2f.gif";
 	    img2off = new Image();  img2off.src = "images/folderboat2f.gif";
 	    img3off = new Image();  img3off.src = "images/folderbooking2f.gif";     

        }
    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");                    }
    }