I'm not real keen on the idea only because of the lack of effeciency in 12+yr old CPU design. A quick guesstimation puts almost 2kW/h draw out of those 12 units. I'd much rather see that built from 12 Raspberry Pi's. In my guesstimations here, the $420 worth of Pi's (12 @ $35 each run at about 6W each) would pay for themselves rapidly if compared with the power usage of the PII's.
Just my take on the idea