function preload(img)
{
   img = new Image();
   img.src = img;
}

function animate()
{
   document.images.jumper.src='../images/jump.gif';
}

function unanimate()
{
   document.images.jumper.src='../images/jump_static.gif';
}

preload('../images/jump.gif');
preload('../images/jump_static.gif');