Here is the RTL8139/810x Driver for Snow Leopard. ITS FOR ONLY x64 BIT PC's / Mac's. Enjoy
Hi.
Replace the AppleRTL8139Ethernet.kext from the Original IONetworkingFamily.kext with the AppleRTL8139Ethernet.kext from the OSX86 site.
Location : /System/Library/Extensions/IONetworkingFamily.kext/Contents/Plugins/AppleRTL8139Ethernet.kext
And then
Put your modified IONetworkingFamily.kext into /S/L/E.
Run "Kext Utility".
Reboot.
JACKIEBOY8!!!!!!!!!!!!!!!
UPDATE: I just installed Lion (x64 DUH) and you just need to open this kext and go to the plug in folder and copy the RTL8139 plugin to the IONetworkingFamily.kext in Lion / System / Library / Extensions and past it in the plug in folder. Run my latest uploaded version of kextutility or use kextwizard to repair permissions and reboot. Now you have it fully working!