if (document.images) {         
            img1on = new Image();      
            img1on.src = "i/s_boes_on.gif";
            
            img2on = new Image();      
            img2on.src = "i/s_db_on.gif";
            
            img1off = new Image(); 
            img1off.src = "i/s_boes_off.gif"; 
            
            img2off = new Image(); 
            img2off.src = "i/s_db_off.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");
        }
}