if (document.images) {         
            img1on = new Image();      
            img1on.src = "i/arrow-lr.gif";
            
            img2on = new Image();      
            img2on.src = "i/arrow-rr.gif";
            
            img3on = new Image();      
            img3on.src = "i/arrow-llr.gif";
            
            img4on = new Image();      
            img4on.src = "i/arrow-lrr.gif";
            
            img1off = new Image(); 
            img1off.src = "i/arrow-lgr.gif"; 
            
            img2off = new Image(); 
            img2off.src = "i/arrow-rgr.gif"; 
            
            img3off = new Image(); 
            img3off.src = "i/arrow-llgr.gif"; 
            
            img4off = new Image(); 
            img4off.src = "i/arrow-lrgr.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");
        }
}