function navClassOn(left, middle, right)
 {
 window.document.getElementById(left).className = "navleft_" + middle + "_ov";
 window.document.getElementById(middle).className = "nav_" + middle + "_ov";
 window.document.getElementById(right).className = "navright_" + middle +"_ov"; 
 } 
 
 function navClassOff(left, middle, right)
 {
 window.document.getElementById(left).className = "navleft_off";
 window.document.getElementById(middle).className = "nav_off";
 window.document.getElementById(right).className = "navright_off"; 
 }