Nope, you only need to have a internet connection!
Well, that means that you have access to the Nintendo Channel where you can download game demos and watch trailers for new games. Downloading the Nintendo Channel is free. You can use it to download game demos for the ds too.
No, you just won't be able to save anything.
You do not need to activate anything on the Xbox 360.
If you have an Xbox360 you can pay to download it. It is not currently available for the Wii or PS3.
You need a internet connection on your Xbox to download games on the marketplace. You could use ethernet but you can also use wifi (wireless).
You need to pay to download games from many services like Direct2drive or amazon or steam or xbla. However, demos, shareware, and freeware games are free.
No, that's not possible. You need to get a capture card, a piece of hardware that will record the visual data.
If xbox360 you need to download something. (Xbox live)
demos of what?, you need more information.
You can play it on Facebook. You don't need to download anything.
You need Internet access to download anything.