Read Instructions Carefully
So, I made a kext for Broadcom NetXtreme BCM5705-A Gigabit ethernet controller.
Works only on 32bit mode.
Device ID: 14E4-1654
How to install:
2) Delete IONetworkingFamily.kext and all kexts for Broadcom ethernet in System/Library/Extensions
3) Drag and drop AppleBCM5751Ethernet.kext and IONetworkingFamily.kext on Kext helper, type your password (for root access) then click on "Easy install"
4) Open disk utility, select your system HDD and click on "Repair permissions"
5) Restart your "Mac"
6) Your BCM5705-A2 is ready
EDIT (31.3.2012): I have uploaded a new script for Snow Leopard.