Google Maps v3 geoXML infoWindow HTML in external DIV example...

map.js

var options = {
	map: map,
	singleInfoWindow: true,
//	suppressInfoWindows: true, // If "false", then no access to infoWindow html. :(
	createMarker: myCreateMarker
};

var overlay = new geoXML3.parser(options);
overlay.parse('http://foo.com/data.kml?v=' + parseInt(Math.random()*99999999));

function myCreateMarker(placemark) {
	marker = overlay.createMarker(placemark);
	google.maps.event.addListener(marker, 'click', function() {
		console.log(marker);
		marker.infoWindow.close();
		var text = marker.infoWindow.getContent();
		showInDiv(text);
	});
};

function showInDiv(text) {
	var sidediv = document.getElementById('contentWindow');
	sidediv.innerHTML = text;
};