// JavaScript Document
var n = 20;
var f = false;
var b = new Array;
function prel(){

   if(document.images) {
  for(i=1;i<=n;i++)
               {str = 'buttons/b' + i + '_o.gif';
               b[i-1] = new Image();
               b[i-1].src = str;
}f = true;
 }
}
function on(im){
if (document.images && (f == true)) 
{document.images[im].src="buttons/"+im+"_o.gif";}

}
function off(im){
if (document.images && (f == true))
{document.images[im].src = "buttons/"+im+".gif";}
}