This is my first post here, and I'm not taking any form of cred for getting the Broadcom BCM57781 working, I did a lot of trial and error with various kexts, manually loading them with kextload, until I got the hang of it with touching, chmod, chown, etc etc.
Until I found this post where basically rccollins posted a working link and a shared some light on how to install it with Kext Wizard.
This is how I did it, and got it to work.
1) Download the file,
BCM57781.zip, from rccollins:
http://www.tonymacx86.com/network/1...m57781-asrock-z77-extreme-4-a.html#post686726
2) Unpack BCM57781.zip on your Desktop (or similar), and you should get a file called IONetworkingFamily.kext
3) Download Kext Wizard from
http://macdownload.informer.com/kext-wizard/3.7/
4) Backup your original IONetworkingFamily.kext from /System/Library/Extensions
5) Delete your original IONetworkingFamily.kext at /System/Library/Extensions
6) Install Kext Wizard
7) Run Kext Wizard and click on the Installation tab
8) Drag the unpacked IONetworkingFamily.kext to Kext Wizard on the white area-window within Kext Wizard.
9) Click on the radio-button System/Library/Extensions
10) Make sure the target disk is your system boot-disk
11) Click on Install and wait a bit
12) Reboot
13) Open System Preferences > Networking
14) Voila
Please comment / provide feedback should you find any errors or similar.
Thanks goes out to everyone who made it possible for the NIC not to work out of the box but I actually had to spend a couple of hours and learned something new