function swapImage (imgId, imgSrc) {
	// imgId can be img object reference or id string
	if (imgId.indexOf && document.getElementById){
		imgId = document.getElementById(imgId);
	}
	imgId.src = imgSrc;
}
function preloadImages () {
	var args = preloadImages.arguments;
	if (!document.pi) document.pi = new Array();
	var j = document.pi.length;
	for (i=0; i < args.length; i++) {
		document.pi[j] = new Image();
		document.pi[j].src = args[i];
		j++;
	}
}
function clearField (fieldId, defaultVal) {
	if (document.getElementById) {
		var ref = document.getElementById(fieldId)
		if (ref.value == defaultVal) ref.value = '';
	}
}

preloadImages ('/_images/background_navhover.png');