As an aside, I stumbled across this when looking for a good Pegesus link and wondered how I missed it:

http://en.wikipedia.org/wiki/Civilian_Space_eXploration_Team
 

Pretty darned good work for "amateurs."

Burt Rutan designed the first stage of this orbital launch vehicle in the late 80's:

http://www.orbital.com/SpaceLaunch/Pegasus/

It will be interesting to see if he is asked to come up with something by Virgin...if he already hasn't.