This KEXT enables most Broadcom 4300 series wireless adapters to work as Airport. I have used this on a couple different setups.

Installation involves several easy steps.
1. Place the file Broadcom43XXFamily.kext into your /Extra/Extensions folder (see below if you do not have an /Extra/Extensions/ folder)
2. This driver has dependencies on the IONetworkingFamily. This means you need to install that .kext as well. Go to /System/Library/Extensions/ and find IONetworkingFamily.kext and copy (using copy and paste) it to the desktop. (You cannot usually paste directly to the /Extra/Extensions/ folder due to permissions blocking that action.
3. Drag the IONetworkingFamily.kext from your desktop to /Extra/Extensions/.
4. Restart. Your card should be automatically detected.

If there is no /Extra/Extensions, just a file called Extensions.mkext, you will need to first create a folder called Extensions in Extra, then open and extract the contents of Extensions.mkext and place the contents into Extra/Extensions. Then remove Extensions.mkext (don't delete it, just move it to the desktop, you may need it later)

(Optional) If you desire, you can also place the Broadcom43XXFamily.kext into your /System/Library/Extensions, but I have not found this to be any more reliable or stable than just locating it in the /Extra/Extensions folder, and there is always the potential for a conflict if you modify your system. Add the file by dragging it onto KextHelper.

The following Chipsets should be supported

BCM 4306
BCM 4309
BCM 4311 (Natively Supported)
BCM 4315
BCM 4318
BCM 4320
BCM 4321
BCM 4322
BCM 4323
BCM 4323x Family
BCM 4324
BCM 4325
BCM 4326
BCM 4328
BCM 4329
BCM 4342

The following card models should be supported

Belkin F5D7000
Buffalo WL12-PCI-G545
Linksys PCMCIA Card WPC54G
Dynex DX-BNBC
Dynex DX-BGDTC
Netgear WN311B (v1 & 2)

Probably tons of other cards, as long as they have a supported chipset...

I take no special credit for this KEXT. Even though I have written this KEXT and made this available to the community, this hack can be done by anyone with a text editor and a little know how. My goal here is to make a KEXT available to the community that can be installed and will work on as many Broadcom chipsets as possible, and to do it in a Vanilla friendly way.

Added experimental rev2 kext which might add support for more cards. Still, if your card is not on the list or has a chipset not on the above list, don't be surprised if it doesn't work. If it does work, please post your Brand, model number, version number, and chipset.