i have the same (onboard) card like you
RTL8111B/C PCIE Onboard
and i use the standard forcedeth kext (that is bundled with kalyway and zephyroth's release)

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HomeHackintosh:
AMD Athlon64 X2 4400 :: ASRock ALiveNF5-eSATA2+ R3.0 :: Corsair 2GB DDR2-800 :: Gainward Geforce 8800GS PCI-E :: Maxtor 250GB SATA HD :: Audiotrak Maya 44 USB :: Phillips 22" 220AV TFT ::
Custom 10.5.5 Voodoo_Beta2 Kernel

Minimacbook:
Acer Aspire One A150X Netbook :: Intel Atom 1,6Ghz :: 1GB DDR2 :: Seagate 120GB SATA HD :: Acer 8,9" Crystal Bright TFT ::MSI Wind OSX 10.5.4 upgraded to 10.5.5 & Voodoo_Beta2 Kernel