Are you thinking of something along the lines of the SETI project, perhaps? In that, the satellite processors don't really "give" their power to the central PC - the central PC just divides up a million tasks and gets one or other satellite to process the data in its own time at a normal rate, then send back the answer. There's probably someone there who'd explain the bones of the system to you if you asked in the right way...

What I do with my old boxes is crude but effective - allocate certain machines for certain uses, and share the power by not clogging up a good machine with stuff doesn't need to be there. Programs that don't need much in the way of resources go on the old, slow machines - e.g. I do virtually all of my html editing in wordpad, so an old 486 is fine for that; archives get stored on daisychained HDs salvaged from boxes with dead motherboards; etc, etc.

All in all, though, you'll just be wasting electricity, keeping five machines going at the same time unless you've got a good project for them to be working on. If they're in working order, you'd be better off passing them on to someone who can use them.