No, really. You cant' put two computers together to combine their processing power... you could set up a rendering farm, but that only works for very specialised applications like rendering (surprise, surprise) or compiling programs. The best you could do is swap the components around so you get the most powerful components of both machines into one, could be as simple as pulling out all RAM and adding it on the other computer (if they're the same type, of course).
What are the specs of these two computers you're talking about?
Na,, but seriously man, it can be a leghnthy process, especally if yo don't know, or haven't done it before, not worth it imo, unless you have a bunch of computers. Just google it, you'll get some responses.