mobo quad socket -
http://www.newegg.com/Product/Produc...82E16813151085
16 cores, cpus 4x
http://www.newegg.com/Product/Produc...82E16819105199
SSD - 4x or so
http://www.newegg.com/Product/Produc...82E16820167005
Power Supply
http://www.newegg.com/Product/Produc...82E16817703022
few of these HDD
http://www.newegg.com/Product/Produc...82E16822136322
Case -
http://www.coolerguys.com/llpcv2010.html (black ;p)
16G or so ram, whatever's compatible in the mobo manual.
Decent nVidia video card or two.
And whatever other small stuff.
That system would smoke any mac ever made and maybe even cost less or at least it wouldn't be much more.