There's a discussion about this somewhere else around here in another thread, but to answer your question, your best bet is to get credit on both airlines!

Getting credit on USAirways should be easy. You should have just given you frequent flyer number when checking in, but having not done that, you should go about claiming the missing credit in a typical manner.

As for Continental, you should be able to get credit on them also by sending them a letter explaining that they rebooked you on a different airline and you'd really like to get the Continental miles.