Exemplo (veja o
Como fazer...)
Code.aspx
<cc1:GMap ID="GMap1" runat="server" />
Code.aspx.cs
GMap1.addControl(new GControl(GControl.preBuilt.GOverviewMapControl));
GMap1.addControl(new GControl(GControl.preBuilt.LargeMapControl));
GMarker marker = new GMarker(new GLatLng(39.5, -3.2));
GInfoWindow window = new GInfoWindow(marker, "<center><b>GoogleMaps.Subgurim.NET</b></center>", true);
GMap1.addInfoWindow(window);