I just put 2 PC's online doing this, and have 7 more that I could use, except no place to set them all up. I'll probably set up 1 or 2 more for this project.
I think most of us, once we take a full accounting of our old CPU inventories, are a bit surprised by how many machines we have collected over the the years. I know I was. By simply adding a cheap wireless access point to the end of a broadband connection, and cheap WLAN cards or USB units to the old machines, many if not most of the old machines can be put to profitable use folding protein.