You can geocoding this way:
GMaps.geocode({
address: $('#address').val(),
callback: function(results, status){
if(status=='OK'){
var latlng = results[0].geometry.location;
map.setCenter(latlng.lat(), latlng.lng());
map.addMarker({
lat: latlng.lat(),
lng: latlng.lng()
});
}
}
});
You can define either address or lat and lng. Also, you must define callback, which will use results of geocoding and status.