System components:

• D945GCLF2D Mainboard
  

  Intel Corporation 82945G/GZ Integrated Graphics Controller [8086:2772] (rev 02) (prog-if 00 [VGA controller])

  
  

  Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller [10ec:8168] (rev 02)

  
  

  Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller [8086:27d8]

  
  

  Intel Corporation 82801G (ICH7 Family) IDE Controller [8086:27df] (rev 01) (prog-if 8a [Master SecP PriP])

  
  

  Intel Corporation 82801GB/GR/GH (ICH7 Family) SATA IDE Controller [8086:27c0] (rev 01) (prog-if 8f [Master SecP SecO PriP PriO])

• SATA 250GB SAMSUNG SP2504C (only one partition GUID)
• IDE DVD-RW HL-DT-ST DVDRAM GSA-4167B
• ASUS VK222 connected through VGA, 1680x1050@60Hz
• USB keyboard and mouse

BIOS Settings:
1. Main:

• Intel Hyper-Threading Technology <Disable> 1

2. Advanced - Boot Configuration:

• Numlock <On>
• System Fan Control <Disable>
• System Fan Speed <50%>
• Max CPUID Value Limit <Disable>
• Display Setup Prompt <On>

3. Advanced - Peripheral Configuration:

• Serial Port <Disable>
• Parallel Port <Disable>
• Audio <Enable>
• High Definition Front Panel Audio <Enable>
• Legacy Front Panel Audio <Enable>
• On-board LAN <Enable>

4. Advanced - Drive Configuration:

• Use Automatic Mode <Enable> 2
• ATA/IDE Mode <Native>
• S.M.A.R.T. <Enable>
• Hard Disk Pre-Relay <0>

5. Advanced - Event Log:

• Clear Event Log <Disable>
• Event Logging <Disable>
• Mark Events As Read <Disable>

6. Advanced - Video Configuration:

• DVMT Mode <DVMT>
• IGT DVMT Memory <128 MB>
• IGT Aperture Size <256 MB>
• Primary Video Adaptor <Auto>

7. Advanced - Memory Configuration:

• PCI Latency Timer <32>
• HPET <Enable> 3

8. Advanced - Management Configuration:

• ASF Support <Enable>

9. Advanced - USB Configuration:

• USB Ports <Enable>
• USB 2.0 <Enable>
• USB Legacy <Enable>

10. Security:

• Expansion Card Text <Disable>
• XD Technology <Enable>

11. Power:

• After Power Failure <Stay Off>
• Wake on LAN from S5 <Power On>
• ACPI Suspend State <S3 State>
• Wake on LAN from S5 <Disable>
• Wake on LAN from S5 <Keyboard 1>

11. Boot - configure by yourself

Known issues with BIOS settings
1. "Should have 2 cores, but only found 1":
try to disable HyperThreading in BIOS. Also NullCPUPowerManagement.kext can help you.
2. Kernel panic with "... IOATAFamily ..." & "Secondary IDE channel is disabled":
a. you can set Use Automatic Mode to <Disable> under Drive Configuration section in BIOS, then Primary Channel option will be enabled and you should set it to <Disable>. Warning! Disabling primary channel in BIOS will disable any device attached to IDE port - use it only if you have SATA optical drive or you are installing from USB.
b. also you can place DSDT.aml to the root of your drive and it will overcome that error.
3. "HPET device is not available":
set HPET to <Enable> in Chipset Configuration
4. "...IOACPIFamily..." & "...IOPCIFamily..." kernel panic:
your DSDT is probably broken - I had an issue with Store(Package (0xA7) { ... } when only 3 child nodes were inserted, therefore Package(0x06) must be written. Funny, but same DSDT was working until I updated my system to 10.6.2.

Where to start
Well, I know that everyone loves retail, but be honest - without knowledge of subject (OS X in case) you will never set up retail, so try to install custom distributives for first time. I recommend Mac OS X Snow Leopard Universal by dan1234.
Search for earlier versions with 10.6.0 only, because testing of his latest 10.6.2 build shows some minor errors and you will be forced to apply 10.6.2 update again to get rid of them.
So, you have downloaded and burned iso to single-layer DVD. Start with HyperThreading disabled in BIOS and with USB peripherals, PS/2 is to old for OS X. Now you should boot and right after choosing setup language go to Utilities - Disk Utility. Now you should repartition your hard drive. If you are a newbie - just select hard drive (not partition), go to Partition tab and change Volume Scheme: "1 Partition" with Format: "Mac OS Extended (Journaled)". All data is erased, you know have a clean volume and can move on. Close Disk Utility and follow wizard's steps.
*Under Options... button in Partition tab you can choose GUID (OS X native) or MBR (Windows-compatible, use if you plan to dual-boot) disk types.
Attention! "Customize" your installation before pressing "Install" because system will not boot after reboot. In Customize window you should select NullCPUPowerManagement -or- Disabler (will be removed after applying DSDT), IOATAFamily (again, doesn't really needed if you already have DSDT.aml in root of your hard drive), fakeSMC -or- dsmos (do not ever remove this, replace with newer version instead). There you have it. After reboot you can reach desktop so just drop DSDT.aml in root of your hard drive and update your kexts along with your kernel. All job will be done by DSDT but for restart you should use EvOrestart.kext, VoodooHDA.kext will give you sound, and com.apple.Boot.plist with smbios.plist placed in /Extra will turn your Unidentified PC to MacMini.
If you want HyperThreading - place new kernel (links below) in /, update your system and boot with kernel=your_HT_kernel_name flag.

Things explained
Why do I recommend distributives? I want you to reach OS X desktop as soon as possible. System will not start without DSDT+patched kernel or NullCPUPowerManagement+IOATAFamily. So you install distributive and choose those two extra kexts. After installation you can place your DSDT and move those kexts away and maybe delete them if you know what you're doing. Then you can update kernel, turn HyperThreading in BIOS and install additional kexts (VoodooHDA, EvOreboot).

Why you should not replace your kernel or delete some kexts
Do not replace kernel! Name your kernel as you wish except mach_kernel and place it in /. Why?
Say Apple releases new update 10.6.3 for example. You apply this update which contains a new kernel and it replaces kernel you already have. You reboot your hack and nothing works. But if you have your kernel named my_kernel then you can set

in com.apple.Boot.plist or pass kernel=my_kernel command at boot. Then you boot your kernel even if vanilla mach_kernel updated.
For that reason, it is good to have your kexts in /Extra/Extensions folder. Because /System/Library/Extensions gets updated by Apple from time to time.

What to do if system gives you kernel panic
D945GCLF2 is guaranteed to work with NullCPUPowerManagement, IOATAFamily patches and HyperThreading disabled in BIOS. If you want HyperThreading - get appropriate kernel (do not name it as mach_kernel - read paragraph above). If you want to get rid from NullCPUPowerManagement - place DSDT.aml in / and move NullCPUPowerManagement to /Backup for example. Then if things go wrong you can always boot from DVD and go to Utilities - Terminal. Then you can execute following commands:

In that way you can place your kext back where it was.

Useful kexts
I will try to keep links up-to-date but your better follow blogs of authors. I will credit them later.

1. I highly recommend PC_EFI 10.6 bootloader and fakeSMC.kext by netkas. This stuff gets updated from time to time so you better follow his blog instead of using direct links. Those two things will give your proper boot and decrypting of some "do not ever steal mac operating system" kexts. It is critical to have that installed.
2. NullCPUPowerManagement.kext, EVOReboot,kext, SleepEnabler.kext & VoodooHDA.kext are available at kexts.com. Keep in mind that not all of those kexts are needed. For example, NullCPUPowerManagement is no longer needed in 10.6.2 because of teateam's kernel and SleepEnabler no longer needed because we got native AppleIntelCPUPowerManagement support and system sleeps fine in 32-bit mode.
3. Patched 10.6.2 kernel (with Intel Atom support and HyperThreading) is available here.

Credits
teateam, prasys, netkas, The KiNG, ugokind, nok6230, modbin, StellaRola

DSDT
Far from perfect, but many things fixed. Intel Atom doesn't support SpeedStep but I've got one in DSDT - just to evaluate some warnings at boot. Also there is WiFi injected - you may delete that too.
Solution doesn't include 10.6.2 HyperThreading kernel - get it from tea's blog. place kexts to /Extra/Extensions, other files to /Extra.