The amp bypass from crutchfield.com is the easiest way to do it.
It cuts the factory amp out of the factory wiring loop. You plug into the factory wiring after the factory amp with the supplied wire harnass.
It sells for $20 and is worth every penny, especially the detailed instructions and color-coded wiring for the novice installer.
Rewiring all of the speaker wiring in the car is waste of time unless you're pushing some component speakers with some serious juice.
Just make sure to get the amp bypass and not the amp integration kit. Like cruises8 said, it'll sound like crap if you don't bypass the amp.
