Did you integrated LAN driver to your build?. You can add a single driver or a generic driver collection like the one from "driverpacks.net".
First you should select "PEnetwork" under componenets section. Select "autostart", "enable IP auto configuration" tick boxes (assuming no static IP).
Secondly you need to select a web-browser. You can choose between either IE (under components section) or Opera (under apps--->network)
Thirdly you need network driver to be available at boot. DISM driver integration is my choice.You can use "drivers-->driver integration" script to add LAN drivers. Either copy your unpacked broadcom driver or extracted "Driverpack LAN" to the "Workbench\Common\Drivers_x86" folder. You can open that folder by clicking "explore" button in the "driver integration script".
Link to the 32bit LAN driverpack :
http://driverpacks.net/driverpacks/windows/7/x86/lan/12.08Use 7zip to extract and copy the main folder to the driver integration directory.