Yah, the battery should be in the trunk, passenger side, under some plastic stuff, thats where you want to put the amp, the stock amplifier for your car is on the driver side, underneith some really stiff-ass carpeting.
If you really need to run to the engine bay anyways, if you remove the panel that covers the wires underneith the steering colum, (3 screws, 2 are in plain view in a driving position, the other is underneith) and remove the dead pedal (unscrew the hood latch, and turn a plastic piece with a quarter) there will be a bundle of wires that's wraped with a fabric strap. If the wire isn't huge, you can just cram it through the hole where those wires go, the wire you pushed through will end up in the fusebox. Remove the fusebox cover and unscrew the 4 long screws, carefully pull up the fuse panel and you should see a big mess of wires, and your lone wire stuffed up in there.
You can drill a hole in the fusebox or just run the wire out of a drainage hole or some shit (whatever that is) like I did.
If you need a high amperage positive terminal to tap off of, you can use the one on the right side of the engine bay.