If you are one of the many people experiencing AirPort connectivity problems after upgrading to 10.5.8, here’s a solution that worked for me, found on the Apple Discussions forums from user SpacePirate.
This solution allows you to revert to the 10.5.7 AirPort kernel extension (kext file) without reverting the entire OS back to 10.5.7. It appears that Apple is aware of the problem, so hopefully we’ll see an update soon that fixes this bug.
It’s worth emphasizing that you should not do this unless you are comfortable modifying system files. Ensure you have a good backup. Proceed at your own risk.
– Download the 10.5.7 Combo Update.
– Download and install Pacifist, a handy tool that allows you to extract specific files from an Apple package (i.e. the Combo Update is a .pkg file).
[Pacifist is $20 shareware. You can use it in trial mode to accomplish this task, but if you think it’s something you might use from time to time, consider buying it. It’s helpful for repairing damaged files without reinstalling the entire OS, verifying installations, and finding missing or altered files.]
– Turn off your AirPort.
– Delete /System/Library/Extensions/AppleAirport.kext.
– Delete /System/Library/Extensions/IO80211Family.kext.
– Extract /System/Library/Extensions/AppleAirport.kext from the 10.5.7 package using Pacifist and copy this file to the /System/Library/Extensions/ folder on your Mac.
[Open the 10.5.7 package with Pacifist, find the AppleAirport.kext file in the /System/Library/Extensions/ directory of the package, and extract this file to your /System/Library/Extensions/ folder on your Mac, or copy the file to the desktop, then drag it to the /System/Library/Extensions/ folder on your Mac. Don’t try taking these files from a Time Machine backup unless you know how to properly set permissions for the copied files. If you use Pacifist, the app will set the correct permissions for you.]
– Extract /System/Library/Extensions/IO80211Family.kext from the 10.5.7 package with Pacifist using the method described in the previous step.
– Delete the /System/Library/Caches/com.apple.kernelcaches/ folder.
– Delete /System/Library/Extensions.mkext.
– Empty your trash. Reboot.
– Turn the AirPort back on.