The General idea of what Yochdog said is about right. You could do it but it be very expensive.
Bitcoin "mining" started on CPU's, but it then moved on to GPU's once code was modified and specialised to work on them.
FPGA's in the last year or so, improved upon what GPU's could do, with less power used, again modifying the code to work on them.
ASIC are this year just starting to improve on what FPGA's did. Each time getting faster and using less power.
Each change, made them more efficient. CPU's now compared to ASIC's is like comparing a Bicycle to a Jet Fighter in terms of speed.
ASIC is the latest Tech, going back even 2 steps in mining would be horribly expensive to do those sort of numbers, with GPU's.
Even a modern rendering (ATI gpu) farm would not be that efficient, other than it would be more likely to have a half decent resale value.
An ASIC or FPGA now a days is still the best thing to get, going backwards is not cost effective unless under unusual situations that effect your bottom line of costs.
Before spending any money, especially a lot, the wiki is a worthwhile read.
https://en.bitcoin.it/wiki/Main_Page
