img1 = new Image(); img1.src ='img/btng1.gif';
 img2 = new Image(); img2.src ='img/btng2.gif';
 img3 = new Image(); img3.src ='img/btng3.gif';
 
 img4 = new Image(); img4.src ='img/btno1.gif';
 img5 = new Image(); img5.src ='img/btno2.gif';
 img6 = new Image(); img6.src ='img/btno3.gif';
 
 function menu_off(x1,y1,z1)
 {
  document.getElementById(x1).src=img1.src;
  document.getElementById(y1).style.background='url('+img2.src+')';
  document.getElementById(z1).src=img3.src;
 }
 function menu_on(x,y,z)
 {
  document.getElementById(x).src=img4.src;
  document.getElementById(y).style.background='url('+img5.src+')';
  document.getElementById(z).src=img6.src;
 }