Before you dive into the laptop, make sure that the wireless is not disabled in windows or the BIOS, or at least check the color of the wireless indication light. Green means that the wireless is enabled.
Well, that depends on the severity of the damage. If the switch itself has been broken off of the motherboard, then you better have some soldering skills. Generally the weakest point is the small plastic piece protruding from the switch on the motherboard where the Wi-Fi catcher meets it. Opening the laptop to reveal that switch means you have to take of the top cover to get to it, so it will take a little time to get to it, and you will have to turn on the computer with the cover off to initialize the wireless due to the digital momentary switch. Once the system is on you can use a pin or precision flathead to turn on the wireless and then simply close up the laptop again.