if (document.images) {
	 b_lo = new Image();b_hi = new Image();
     b_lo.src="img/b_lo.gif";
     b_hi.src="img/b_hi.gif";  
	}         

  function Roll(ButtonObject, ButLo) 
    {if(ButLo && document.images) ButtonObject.src = ButLo.src;}