Since no one bothered to answer your question yet, I'll give it a try.
First have a look at this:
1 and 2 are your processors.
They process tasks they get from Number 4, called "Advanced PowerPC G5 System Controller".
If one processor is busy with a task, the system controller will give the next task to the other processor. This will improve your computers performance, since one processor doesn't have to do two tasks at the same time.
If you simply check your e-mail and surf the internet once in a while, you won't see the difference between a single and a double processor computer.
But if you want to do some work on it, in photoshop or movie edit program you'll see the difference. Cause some 3d-programs and photoshop filters have the ability to use both your processors to complete one task wich will give it a great speed boost. Some futur games will have dual-processor ability aswell.
