Here goes my way to solve the networking issues. Pay attention freebazee1, hopefully this will help!

It looks like a lot, but every single step is there for newbies. It'll take about 5 minutes.
- Leave IONetworkingFamily.kext untouched. Don't put in any kexts and don't edit it. Don't need it. Just delete anything which is AppleBCM57*** in S/L/E and also in S/L/E/IONetworkingFamily.kext. Run Kext Utility after deleting anything and reboot.
- Unzip and put in the BCM5722.kext directly into S/L/E (NOT in IONetworkingFamily.kext) that I've attached below.
BCM5722D.zip 44.54K
47 downloads
- Run Kext Utility.
- Reboot. You should be have booted with no problems, no hangs and have a network connection but you most probably won't get an IP address. That's fine!
- Type 'ifconfig' in terminal and make a mental note of which one your ethernet is. Most probably en0.
Next the script that sets your correct MAC address and will make sure the kext works perfect when your turn your server on.
1. Open Terminal (/Applications/Utilities/).
2. Type: cd /Library
3. Press Return.
4. Type: mkdir StartupItems
5. Press Return. (If you encounter an error, continue to step 6.)
6. Type: cd StartupItems
7. Press Return.
8. Type: sudo mkdir MACADD
9. Press Return.
10. Type: cd MACADD
11. Press Return.
12. Type: sudo pico MACADD
13. Press Return.
14. In the pico editor, paste in the following text making sure that you've edited the network interface (en0, en1 etc if you need to) and change xx:xx:xx:xx:xx:xx to your mac address.
#!/bin/sh
. /etc/rc.common
##
# Configure a network interface MAC Address setting
##
#
# This script will set the MAC Address setting for the specified interface(s)
#
# The name of the interface (ex. en0) must be edited to match the interface
# to which the MACADD setting should be applied
#
##
StartService ()
{
ConsoleMessage "Configuring MACADD"
### uncomment lines and change the value following 'ifconfig' as appropriate for network interface and mac address
if [ "${MACADD:=-NO-}" = "-YES-" ]; then
/sbin/ifconfig en0 lladdr xx:xx:xx:xx:xx:xx
/sbin/ifconfig en0 down
/sbin/ifconfig en0 up
fi
}
StopService ()
{
return 0
}
RestartService ()
{
return 0
}
RunService "$1"
15. When you have finished customizing the file, save it (press Control-O), press Return, and exit pico (press Control-X).
16. Type: sudo chmod 755 MACADD
17. Press Return.
18. Type: sudo pico StartupParameters.plist
19. Press Return.
20. In the pico editor paste in the following text (no editing required!):
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Description</key>
<string>Can set MACADD</string>
<key>OrderPreference</key>
<string>None</string>
<key>Provides</key>
<array>
<string>MACADD</string>
</array>
<key>Requires</key>
<array>
<string>Network Configuration</string>
</array>
</dict>
</plist>
21. Then save it (Control-O), press Return, and exit pico (Control-X).
22. Type: sudo chmod 755 StartupParameters.plist
23. Press Return.
24. Type: sudo pico /etc/hostconfig
25. When prompted, enter your password and press return.
26. In the pico editor, add this line at the bottom:
MACADD=-YES-
27. Save it (Control-O), press Return, and exit pico (Control-X).
When you restart the computer, your specified MAC address is set for the interface that you specified. Check it by typing ifconfig in terminal.
Notes
1. The MACADD will be reset after changing a Location, waking the computer from sleep, or changing the state of the network interface. To use the script again without having to restart, enter the following command:
sudo SystemStarter start MACADD
2. If you experience any issues or wish to not set MACADD during startup, you can turn off the new script by changing the MACADD line in /etc/hostconfig to:
MACADD=-NO-
DONE! 
Everything should be set up and working fine.
freebazee1, on Aug 6 2011, 08:22 PM, said:
Here is what I did up till now-
- Installed SL and updated to 10.6.8 (without USB rollback as it froze the USB and I had to reinstall everything)
I had the same issue but the USB rollback should really be done otherwise you might come across problems later on. I didn't do the rollback, didn't think it was necessary until I got a kernel panic when I plugged in a USB stick and it all froze. It's a bit random. But Multibeast didn't do the rollback for me either so use the following kexts I've attached. Install them with Kext Wizard
Download Kext Wizard, select both kexts and tick the box which says System/Library/Extensions. And install and then repair permissions etc as normal when doing anything with the extensions folder. It's how I did it

The reason why it froze the USB was that Multibeast deleted the IOUSB kexts but then didn't replace them so the USB stopped working.
USB_rollback_kexts.zip 1.11MB
28 downloads
Hope all that helps someone!
tk007b - Give my ethernet method a try, won't take long and the kext is a tad more stable along with the auto mac address setting which is a cleaner method!
Credits
The BCM5722D kext - credit goes to adlan. I just edited the device/vendor ID into the kext so it'd recognise our ethernet card.
The MACADD method - Copied it from somewhere and I've edited it to update it a little for our N36L. I believe the guide was written by Apple! I've just edited it.
The USB Rollback kexts - They're the ones multibeast provide. Someone attached them to a post - can't remember who!
Sorry for the VERY long post! Just wanted to share what I've learnt/done

Let me know how it goes