Hardly. Any 5000 series ati card will easily make a profit. The 5770 is a decent buy, costing roughly $100 or so, and can get around 230 mhash/sec.

OP, even if you're running the computers constantly anyway, the strain on the cpu isn't even worth 180 khashes. Don't forget that a fully loaded cpu also uses more electricity than an idle one. I highly doubt you'll actually see any profit.