You must enable Test Mode to load the unsigned driver:

While this guide will get your Broadcom BCM430N working on Windows 7, you must consider the limitations:

Windows 7 is trying to use a signed driver that conflicts with another Broadcom component (usually the Bluetooth or Card Reader).

Since Broadcom primarily provides chips to manufacturers (OEMs), the safest way to find the driver is through your computer manufacturer’s support site. Broadcom Wireless Driver for Windows 7 (32-bit and 64-bit)