if (document.images) {
img1on = new Image();	
img1on.src = "menu/button1_over.gif";
img2on = new Image();
img2on.src = "menu/button2_over.gif"; 
img3on = new Image();
img3on.src = "menu/button3_over.gif";
img4on = new Image();
img4on.src = "menu/button4_over.gif"; 

       
img1off = new Image();	
img1off.src = "menu/button1.gif";
img2off = new Image();
img2off.src = "menu/button2.gif"; 
img3off = new Image();
img3off.src = "menu/button3.gif";
img4off = new Image();
img4off.src = "menu/button4.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");
        
                                }
       }