is what this is called. But you won't be able to do it with your normal stock OS.
You can find a very good example in google server farms, for example. Recently I read that to handle one search request, 700 to 1000 machines are doing something.
Is it even possible to pool several computers' resources, not just the files on hard drives but even cpu power and ram, together on a network? I ask because we have several extremely old Windows computers XP that separate are practically useless but, if there somehow connected to work in harmony with each other, could prove of some value. Is there some term or phrase I can google that could give me more info?