Some thoughts to add to Manda's post about networking.
Rather than have redundant runs in case of failure, use conduit in cavities and leave a pull-though in each. This also leaves the way open for upgrades.
I am concerned by the number of people who plan to use their garages for locating their modem, router and/or server. Often garages are not insulated, and the temperature on hot days can easily exceed the maximum temperature ratings for these devices. (Dlink rate many of their devices to operate up to 40 C. Garages can exceed 50 C on hot days.) We have already owned a UPS and a modem that would fall over in hot days inside our house without exposing them to the temperatures that garages experience.
Relying on a weak signal outside the house to increase security of a wireless network troubles me a little. It is relatively easy and cheap to buy or build a high gain directional antenna that would overcome this. If you don't know how to set up a home wireless network securely, than pay for someone to do it for you. The consequences of not having a secure network, as Manda says, are too high to not get this correct. (Use proper encryption, decent passwords on the modem and router, and specify the network card IDs that can access your network.)