if(document.images){
        var imageDir = 'graphics/';
}

if(document.images){

Button1on               = new Image(73,15);
Button1on.src   = imageDir + "bcourses_2.jpg";
Button2on              = new Image(68,15);
Button2on.src  = imageDir + "bdemo_2.jpg";
Button3on               = new Image(155,15);
Button3on.src   = imageDir + "bcustdev_2.jpg";
Button4on               = new Image(67,15);
Button4on.src   = imageDir + "bpricing_2.jpg";


Button1off               = new Image(73,15);
Button1off.src   = imageDir + "bcourses.jpg";
Button2off              = new Image(68,15);
Button2off.src  = imageDir + "bdemo.jpg";
Button3off               = new Image(155,15);
Button3off.src   = imageDir + "bcustdev.jpg";
Button4off               = new Image(67,15);
Button4off.src   = imageDir + "bpricing.jpg";


}

function imageOver(name){

  if(document.images){
    if(lastButton) {
      document[lastButton].src = eval(lastButton + "off.src");
    }
    document[name].src = eval(name + "on.src");
    lastButton = name;
  }
  return true;
}