Hi Ryan,
CMEs interact very strongly with the Earth's magnetic field but how it interacts depends strongly on the orientation of the magnetic field in the CME. The Earth's magnetic field essentially points from south to north. If the field in the CME points the same way then the CME just compresses the Earth's magnetic field with nothing much happening other than a strengthening of the measured magnetic field at the Earth's poles and some faster motions of the plasma in the magnetosphere. If, however, the CME field is southward, i.e. opposite that of the Earth, then a coupling between the CME and the magnetosphere can occur which transports a lot of energy into the earth's atmosphere. In the most extreme cases, aurora can be seen down to tropical latitudes. For example some large storms in 2003 resulted in aurora being seen to the east of Houston, texas.
David