Have you installed Boot Camp drivers? You need them to make the Wi-Fi and Ethernet cards work.
If you have Snow Leopard, insert the Mac OS X DVD and install the drivers. If you have Mountain Lion or Lion, you have to start into OS X (pressing X key while your computer is starting) and download the drivers on Boot Camp Assistant. See > http://support.apple.com/kb/HT4407 (it applies to Lion and Mountain Lion)