eg_on = new Image ( );
eg_off = new Image ( );
eg_on.src = "images/tk2.png";
eg_off.src = "images/tk_r2.png";

function button_on ( imgId )
{
  if ( document.images )
  {
    butOn = eval ( imgId + "_on.src" );
    document.getElementById(imgId).src = butOn;
  }
}

function button_off ( imgId )
{
  if ( document.images )
  {
    butOff = eval ( imgId + "_off.src" );
    document.getElementById(imgId).src = butOff;
  }
}

if ( document.images )