Scott Sheppard has a well written tutorial on Working with large models and the Google Earth Extension for AutoCAD in his It's Alive in the Lab blog. It turns out that models can be too big to publish to Earth, as described by the blog entry.
His entry also has a link to the user guide that teaches you how to:
- Import Google Earth images into AutoCAD.
- Publish 3D AutoCAD models to Google Earth.
- Drape Google Earth images onto AutoCAD 3D meshes.
- Attach time span information to models.