If you're only going to have G cards on the devices, the N-router isn't going to do anything for you. You'd also have to get N wireless adapters for your devices, otherwise you'll still get G range and speed.
If you do that though, you should be fine. From what I've read, N will actually take advantage of the echos and interference of walls and other obstacles between the router and your devices. Even with a weak signal, you should see better than 100Mbit, which would be plenty for streaming stuff over your network. I've helped someone I know replace his G setup with N and the difference was tremendous. With G his one son was getting almost no signal at all in his bedroom and now he connects back to the router anywhere from 150-200Mbps.
If you're looking for a router suggestion, the one I'm hoping to get for Christmas is
this one. I know the reviews on it aren't great, but they're all related to poor firmware by Linksys and I would be loading
DD-WRT (a 3rd party firmware) onto it anyway which would solve all the problems people are complaining about in the Amazon reviews.