I recently had my MacBook sent in for repair. While I was waiting for it to get back, I booted my backup drive through my Mac Pro so I could continue working. Once I got the MacBook back and I restored from my backup, AirPort refused to turn on. Eventually I found out that Leopard makes a few changes to network device mapping, and doesn't always clean up after itself. It seems that going from one Ethernet port and one AirPort to no AirPort and two Ethernet ports and back again confused it greatly. This thread on Apple Discussions goes over the same problem, in a lot more detail. To work around it, I had to delete AirPort in the Network System Preferences pane and recreate it -- making sure to remove the AirPort icon from the menu bar before hitting apply (restoring /Library » Preferences » Syste...

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