Is there a US broker for Bitcoins? Apparently, there is an Australian trading house, Bit Trade, that will trade currency for Bitcoins or vice versa.

Is there a U.S. equivalent?
There is indeed a US Broker for Bitcoins.  Unfortunately, for now, they're still in private beta.  The company is called Buttercoin: https://www.buttercoin.com/  You can sign up for their private beta, but there's a pretty long waiting list right now.