Official Google Maps API Blog: ExtInfoWindow 1.0: Ajax powered, CSS customization
Have you ever wanted to tweak the look and feel of your map’s info windows? With ExtInfoWindow and a little CSS you can customize your windows to fit the theme of your site. ExtInfoWindow can retrieve content as static HTML strings upon page load, or, for more efficient and real-time data, it can pull data dynamically via an Ajax call when the info window opens. ExtInfoWindow also mimics the behavior of the regular GInfoWindow, panning the map when needed, closing itself when another window opens, etc.