PLEASE NOTE: this tutorial is old, i cannot be sure how much even still works with the latest versions of all the programs listed. http://www.instructables.com/id/Sketchup-3D-modelling-file-conversion-and-advice-/ provides information on 3d modelling and animation with other packages which results in far more advanced video output. That newer tutorial is more likely to be helpful to you than this old one
In this instructable i will show you how to use google sketchup 3d modelling software and wax 2.0 video editing software to add spacecraft and explosions into videos and also how to use wax 2.0 for greenscreen effects. for a glimpse of the effects that can be achieved see the image.
download wax at http://www.debugmode.com/wax/