var n = 2;
var f = false;
var b = new Array;
function prel(){

   if(document.images) {
  for(i=1;i<=n;i++)
               {str = '/buttons/p' + i + '_o.gif';
               b[i-1] = new Image();
               b[i-1].src = str;
}
            f = true;
 }
}
function on(im){
if (document.images && (f == true)) 
{ind = im.substring(3,1);
 document.images[im].src="/buttons/"+im+"_o.gif";}

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