I've given my daughter my old Powerbook G4 - and she loves it - and I don't want to buy a newer laptop. Problem is it will only connect to a 2.4 Ghz network and I would like to have my router only broadcast at 5Ghz. Is there any way to set up a dual band router as a repeater that will receive the 5Ghz signal and broadcast at 2.4Ghz? Or could I use ethernet to wire the repeater to the router and just have the repeater broadcast at 2.4Ghz (they can be close, our home isn't big enough to actually require a repeater)?
Why do you want a second router to broadcast 2.4 GHz? Why not let the router broadcast in 2.4 and 5GHz? I have 2 Airport Extremes both transmitting in 2.4 and 5GHz to cover my full home.
I'ts my understanding that the signal will drop to 2.4 Ghz whenever the MBP is attached to the network. Or does the Airport Extreme have two separate radios?
They use separate radios altogether. The frequency is independent of the speed your network will run at. It may lower the speeds of the 2.4ghz network when that powerbook is connected (a wifi radio will typically only run as fast as the slowest device), but it will not affect your 5ghz network.