This method for customizing the Google Earth Interface, embedding the Google Earth render window (the actual map window) into your own applications, was apparently pioneered Luca Rocchi and his Google Earth Airlines application. Luca figured out that you could grab the GE map window using its Windows handle to place it into your own application. He has used this to plop GE into web applications, but the ActiveX control that he provides for free can also be used in any COM compliant language (such as VB.Net or C#). I have used this plugin (and a similar one of my own design) to access external applications from Google Earth.
This method lets you completely encapsulate Google Earth with your own tools. However, it also hides the Google Earth tools. To get around this, you can assign the entire Google Earth application to be a child to your own custom application. Interestingly, not too long after Luca released his 'Google Earth Airlines' plugin, Google provided a method in their API to directly access the Windows Handle of both the render window (actual map) and the application window (the full application).