function on1() 
{if (!document.images) return; document.a.src = "img/menu_01_a.jpg";} 
function on2() 
{if (!document.images) return; document.b.src = "img/menu_02_a.jpg";}
function on3() 
{if (!document.images) return; document.c.src = "img/menu_03_a.jpg";}
function on4() 
{if (!document.images) return; document.d.src = "img/menu_04_a.jpg";}
function on5() 
{if (!document.images) return; document.e.src = "img/menu_05_a.jpg";}

function off1() 
{if (!document.images) return; document.a.src = "img/menu_01.jpg";}
function off2() 
{if (!document.images) return; document.b.src = "img/menu_02.jpg";}
function off3() 
{if (!document.images) return; document.c.src = "img/menu_03.jpg";}
function off4() 
{if (!document.images) return; document.d.src = "img/menu_04.jpg";}
function off5() 
{if (!document.images) return; document.e.src = "img/menu_05.jpg";}

var imgslist = new Array(
"img/menu_01_a.jpg",
"img/menu_02_a.jpg",
"img/menu_03_a.jpg",
"img/menu_04_a.jpg",
"img/menu_05_a.jpg"); 

var imgs=new Array(); 
for (x=0; x<imgslist.length; x++) 
 if (document.images) 
  {imgs[x]=new Image(); imgs[x].src = imgslist[x];}