if (document.images) {
  var b1a = new Image(); b1a.src = "images/b1a.gif"; var b1b = new Image(); b1b.src = "images/b1b.gif";
  var b2a = new Image(); b2a.src = "images/b2a.gif"; var b2b = new Image(); b2b.src = "images/b2b.gif";
  var b3a = new Image(); b3a.src = "images/b3a.gif"; var b3b = new Image(); b3b.src = "images/b3b.gif";
  var b4a = new Image(); b4a.src = "images/b4a.gif"; var b4b = new Image(); b4b.src = "images/b4b.gif";
  var b5a = new Image(); b5a.src = "images/b5a.gif"; var b5b = new Image(); b5b.src = "images/b5b.gif";
  var b6a = new Image(); b6a.src = "images/b6a.gif"; var b6b = new Image(); b6b.src = "images/b6b.gif";
  
  var bnexta = new Image(); bnexta.src = "images/bnexta.gif"; var bnextb = new Image(); bnextb.src = "images/bnextb.gif";
  var bpreva = new Image(); bpreva.src = "images/bpreva.gif"; var bprevb = new Image(); bprevb.src = "images/bprevb.gif";

  var bxbioa = new Image(); bxbioa.src = "images/bxbioa.gif"; var bxbiob = new Image(); bxbiob.src = "images/bxbiob.gif";
} 
function act(imgName) {
  if (document.images) 
    document[imgName].src = eval(imgName + "b.src");
}
function inact(imgName) {
  if (document.images)
    document[imgName].src = eval(imgName + "a.src");
}