if( document.images )
    {
  but1 = new Image(150, 29) ;
  but1.src = "images/audio-on.gif";
  but2 = new Image(150, 29) ;
  but2.src = "images/audio-off.gif";
}

<!--
function chkVer(imagename,objectsrc)
{
var n=navigator.appName
var v=parseInt(navigator.appVersion)
var browsok=((n=="Netscape")&&(v>=3))
var browsok2=((n=="Microsoft Internet Explorer")&&(v>=4))
if ((browsok)||(browsok2))
document.images[imagename].src=eval(objectsrc+".src")
}
//-->