Also, would it be unethical for me to farm a whole cluster of old Pentium3s/Pentium4s and generate Bitcoins that way?
It would be no more unethical than you getting a cluster of earth diggers together to mine gold. With Bitcoin there is no central authority. Everything is essentially public and only subject to the rules of the free market. Do what you like.
I see you're pretty new, and may think mining coins is easily profitable. It's not. There is a lot of competition for it now. You may want to check out the mining section.
https://bitcointalk.org/index.php?board=14.0