if ( document.images )
{
	var imgLeftOn = new Image;	imgLeftOn.src = "img/btnlefton.png";
	var imgCenter = new Image;	imgCenter.src = "img/btncenteron.png";
	var imgRightOn = new Image;	imgRightOn.src = "img/btnrighton.png";
}

function doPressing( strElement, fIsOn )
{
	var oLeft = document.getElementsByName( "btn" + strElement + "left" )[0];
	var oCenter = document.getElementById( "btn" + strElement + "center" );
	var oRight = document.getElementsByName( "btn" + strElement + "right" )[0];

	oLeft.src = fIsOn ? "img/btnlefton.png" : "img/btnleftoff.png";
	oRight.src = fIsOn ? "img/btnrighton.png" : "img/btnrightoff.png";
	oCenter.style.backgroundImage = fIsOn ? 'url(img/btncenteron.png)' : 'url(img/btncenteroff.png)';
}