PC... why?

Able to do more stronger computational skills. Tell me do Mac's have clusters? I one day look to build my very own cluster. Right now I have a old PC I custom built...

(2x) Intel Xeon X5365 Quad-Core
(6x) Seagates 1TB
ASUS DSBV-DX
12GB Corsair DRR3 RAM
ATI FireGL V5600
(2x) AOC 19" screens
Canon MP-240

OS - Mandriva, & Vista.