How do I set up a network so that the computer I'm on would combine...

[LAPIII]

its usage with the other for better preformance?

An example:

I could network 2 or computers both with dual cores for a quad core experience. Other components can work together too, such as, the motherboads and their chipsets, the GPUs, and memory. The Computers might even be a Mac and the others be PCs

 

[thehelo]

you dont

 

[folken]

Simple answer is no, that is not possible.

While it is possible to "cluster" computers that would not provide the results you are after. Combining computing power is generally only capable of performing few and highly specialized tasks.