If you are going with AMD I would likely pick a motherboard based on the 800 or 900 series chipset. Before buying one though check to see if the network and sound cards for those devices are supported on the osx86 forums. With that done you can pick a processor, Hard Drive, and some memory for it along with buying either a dvd-rw or blu-ray drive (super-multi or burner). The last part to check for drivers for would be a video card best bet would likely be a supported Nvidia or ATI HD5 or 6 series graphics card, but again check the forums for driver support.
When you get your parts and first start your computer go into the BIOS and set the Sata ports to AHCI OR RAID not EIDE Mac OSX does not understand IDE MODE.
I hope this will help you in picking your parts out.
Link to the OSX86 forums -> http://www.insanelymac.com/forum/