GoogleEarth inside Java Swing
There's also NASA's World Wind SDK.
Embedding GoogleEarth inside Java Swing App is not feasible. Legally or otherwise. However you may find a way to embed Google Map on a frame.
Edit: Found this google post.
Even though technically it is possible (using JXMapViewer), legaly it is not. Google does not allow using Google Maps outside of the browser.
One possible solution would be to embed JWebPane (http://weblogs.java.net/blog/alex2d/archive/JWebPaneJ1.pdf) into your Swing App, but it is still not ready :(