alfa = (   ((navigator.appName == "Netscape") 
            && (parseInt(navigator.appVersion) >= 3 ))
        || ((navigator.appName == "Microsoft Internet Explorer")
            && (parseInt(navigator.appVersion) >= 4 )) );

function activateButton(id)
{
    if ( alfa )
    {
	var src  = document.images[id].src;
	var tail = "0.gif";
	if ( src.toLowerCase().lastIndexOf(tail) == src.length - 5 )
	{
	    document.images[id].src = src.substring(0, src.length - 5) + "1.gif";
	    return true;
	}
    }
    return false;
}

function deactivateButton(id)
{
    if ( alfa )
    {
	var src  = document.images[id].src;
	var tail = "1.gif";
	if ( src.toLowerCase().lastIndexOf(tail) == src.length - 5 )
	{
	    document.images[id].src = src.substring(0, src.length - 5) + "0.gif";
	    return true;
	}
    }
    return false;
}