The way computers are made, you can't combine their processing power via hardware. You can only use software to make them command one another in some way, but that will be so inefficient you're better off selling the computers and buying a new better one.

But if you'd like to be the new millionaire who invented a better "cloud computing" solution than VMware or Google have, try your luck.

As the New Yorkers say: Forget-about-it!

Your dealing with different:

processors, speeds, memories, timings, software, hardware, communication, etc.

The best you could do is:

If you had 3 of the same exact computers. One you would use to control and combine the results of the other two computers. This one would need to be programmed to load the particular info into the other computers and then , matching the timing cycles, run those programs. The other computers would need to complete their tasks at nearly the same time [not like to be too hard], signal the first computer that they are ready to send the results to the first computer.The first computer would the need to combine the two results properly and act on them. It is too complicated.

NOTE: Some may argue, that networking computers can do what you want. While yes, networking 1,000s of computers with a certain task can come up with a faster result, the task that the 1000s computers do is a piece of the same larger task, usually mathematics.

I have many old computers laying around my house. I figured there must be a way to combine the processing power of all of them so they act as one powerful unit. I suppose my main computer would be running a program that would split tasks among these smaller computers automatically. Is this possible, or can someone point me in the right direction? I work as a programmer if that means anything to you.