function mostrarBanner() 
{ 

total=3; 
banner = Math.floor(Math.random() * total); 

switch(banner) 
{ 
case 0: 
document.write("<IMG SRC='images/headerHome2.jpg' BORDER='0'>"); 
break; 
case 1: 
document.write("<IMG SRC='images/headerHome3.jpg' BORDER='0'>"); 
break; 
case 2: 
document.write("<IMG SRC='images/headerHome4.jpg' BORDER='0'>"); 
break; 
} 

}