Not exactly what I had expected.
Il Mio Problema
My girlfriends macbook starting having issues connecting to the wireless router. The airport finally lost it's ability to turn on at all. So I had to replace the airport card.
La Mia Riparazione
It all went pretty smoothly until I opened the anti-static bag with the new MacBook Core 2 Duo 802.11 Airport Extreme Card.
Il Mio Consiglio
Upon opening the anti-static bag with the new airport card in it I noticed something.
The new card had 3 little antenna slots for the antenna cables where as the old one only had 2.
I was baffled as to why there was a 3rd antenna port and how to connect it up with the 2 I had available.
I checked online again to make sure I got the recommended hardware from iFixit's Airport repair page for the proper macbook model, I triple checked the model to make sure I was looking at the right one.
I googled a solution and found a few people having the same problem I had but no one had a solution so I was left with trial and error.
The new MacBook Core 2 Duo 802.11n Airport card had 3 antenna ports and I had 2 antenna to connect to it.
Each port was labeled 0, 1 and 2. So I decided to plug the open macbook into the wall and do some trial and error. I plugged in 0,2 at first and that actually worked for a few minutes until it no longer connected and then refused to turn on.
I connected 1,2 and that failed completly. No connection what-so-ever.
I then connected 0,1 and success! The Macbook booted up, connected to one of our wifi networks, I turned the airport off and back on and connected to another network just fine. I rebooted once more just to be sure and it still worked so I closed it up.
TL;DR For those of you using the new Airport card with 3 antenna ports in an old 2 antenna cable system, the ports you want are 0 and 1.