Did you select all the required drivers for your system during installation?

If you want further help, you'll have to give more information on your system such as your motherboards chipset etc.

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 Mac OS X 10.6.4 Retail || Intel Core2 Duo E8200 2.66GHz || Gigabyte G31M-ES2L || GeForce 6600 GT 128MB || Realtek ALC883 Audio || Realtek RTL8169 LAN || Samsung SpinPoint F1 1TB HD || Sony Dual Layer IDE DVD RW DW-D22A || Apple Aluminium Keyboard || Mighty Mouse

 MacBook Pro || 2.4Ghz Core 2 Duo || 200Gb HD || 2Gb Ram || NVIDIA GeForce 8600M GT

 iPhone 4 || 16Gb