if (document.images) { 

    a_on = new Image(); 
    a_on.src = "../images/aboutus_on.gif"; 
    a_off = new Image(); 
    a_off.src = "../images/aboutus_off.gif"; 
    
    b_on = new Image(); 
    b_on.src = "../images/estherdyson_on.gif"; 
    b_off = new Image(); 
    b_off.src = "../images/estherdyson_off.gif"; 
    
    c_on = new Image(); 
    c_on.src = "../images/calendar_on.gif"; 
    c_off = new Image(); 
    c_off.src = "../images/calendar_off.gif"; 
        
    d_on = new Image(); 
    d_on.src = "../images/contactus_on.gif"; 
    d_off = new Image(); 
    d_off.src = "../images/contactus_off.gif"; 
    
    
} 

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

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