I've had problems with included AppleYukon2 kext on 10.5.1 leo. Same thing with 10.5.2. Ethernet card kext works... but the speed... reminds me of long ago dial-up times. So I've installed the kext from 10.4.8 tiger where it worked great. And it still does on leo.

You might wanna try too... Just find "IONetworkingFamily.kext", look up its contents - there'll be "plugins" with "AppleYukon2.kext" inside. Just back it up and move it to trash (or remove completely if u like). Put the attached here "AppleYukon.kext" instead. Run the "kext helper" utility, drag the "AppleYoukon.kext" in the main window, click "easy install", reboot (don't forget the fingercross thing). If the "easy install" button's inactive, u have to have a created earlier admin password - use it.

Here's a "kext helper" link: http://www.cheetha.net/Kext_Helper/Software.html