However, I can sleep my system (Dell D830). See details of the setup on my guide at insanelymac in my sig.

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Dell Optiplex 745 Q965 Chipset
10.5.5 retail /boot-132/ EFI.
System.plist edited to 10.5.6 (needed for iWork'09)
Intel HD Audio ADI1983.
1152x864@32bit ATI (0x1002 0x7187 0x0000) Radeon X1300. Hardware accelerated. QE supported. Can't get my monitor's 1440x900 resolution as in Linux
Network : Atheros 5005G (0x168c, 0x3A1D) card aka Atheros 2413.
Dell Latitude D830 Nvidia Quadro NVS 140M, Suspend works, hibernate/shutdown/reboot don't Snow Leopard