I succeeded in building my own mid range M[h]ac Pro.
Here is the specification list that is confirmed to work.
The motherboard plays the most vital part to successfully run OS X Snow Leopard on a PC.
The guide from lifehacker used a different motherboard but it works on this motherboard nonetheless.
*Another guide specifically for this exact motherboard variant.
The BIOS setup
This is very important. Again, I followed the setup from lifehacker.
Slight Difficulty during the Installation
In the video by lifehacker, the part which you have to choose to boot Snow Leopard from hard disk:
My VGA display just turned black with "Input Not Supported" text shown.
As the video suggested to use the arrow on the keyboard to boot from hard disk, I just tapped the right arrow three times and pressed Enter, ignoring the "Input Not Supported" text.
Surprisingly it worked.
Everything works out of the box, Ethernet, Graphics, USB...etc. except sound.
I got my sound working using the kext (equivalent to driver) from this website.
To install the kext use this software.
M[h]ac Pro updated to 10.6.1 via Apple Software Update website.