function hide_jpg() { 
if (document.getElementById) { // DOM3 = IE5, NS6 
document.getElementById('button_jpg').style.visibility = 'hidden'; 
} 
} 

function show_jpg() { 
if (document.getElementById) { // DOM3 = IE5, NS6 
document.getElementById('button_jpg').style.visibility = 'visible'; 
} 
}