I'm looking for a Green way to backup data on my home network. My wife and I each have computers that are frequently used, plus we have an old computer that we only turn on to stream video to our TV. Currently, I have the old computer also set up as a backup for my computer (which is running linux, so I use rsync). I'd like to also set my wife's computer (running XP) up for backups, requiring her to turn on the backup computer to do so, or leaving that computer on all the time to let it automate backups. I've also considered getting an external hard drive, which could be switched on when necessary, or getting a network attached storage device (NAS, which is more of a mini computer).
In any case, I'd like to be as green as possible with my solution, specifically concerning electricity consumption (both when on and when in standby mode), but also in minimizing buying a lot of electronics.