WORK IN PROGRESS 18th March 2012
It's possible to use certain drivers under linux on a Macbook in order to inject in monitor mode, allowing for much wider greater usage of aircrack-ng.
This was tested on a Unibody Macbook, Mid-2010. That's Model Identifier (go to apple menu → about this mac → more info → system report) of Macbook 7,1. The linux distro used was Ubuntu 11.04.
After getting having set up the ubuntu install, the card was automatically using the Broadcom STA open source drivers, which work great but don't support injection.
Check the chipset: this worked fine on a card with PCI ID of 14e4:4353. This can be found with:
lspci | grep 14e4
Look up your chipset on this page: if it says you can use b43, you're in luck!
I then downloaded and installed compat-wireless. There are already great instructions on their website, so head to this page.
Once that's installed, you'll need to manually install the b43 drivers as we have to compile it with a particular flag telling the system to use this instead of the STA drivers.
You'll need to do:
make B43_BCMA_EXTRA='y'; sudo make install
You'll then have to extract the right firmware for b43 and install that: check these instructions for source installation.
Then you'll have to blacklist the old drivers (you can just blacklist find me), and either reboot for simplicity, or unload and reload the modules. Now check lsmod: if it's all worked properly, you should see b43 listed in there, and your wifi card should be working!
Go have fun with aircrack!