It was a great thread to read. TY. I was planing on adding a Rockford Fosgate amp for the speaker's and a capacitor. When I talk to people at best buy they said they will have to rewire the car and I wont be able to use the the tweeter's any more. I have no clue on how to do this so I was planing on let them do it. If I can do this by myself I would save alot of many any details? And should I do it?
This is the next step up when upgrading audio - def. more time and money. Also, I assume you're not talking about amping the terrible speakers that are already in the car - that'd be a mistake.
The reason you have to re-wire the car is because you run signal wires from the head unit back into the trunk and into the 4-channel amplifier powering your speakers - then you run speaker wires from this amp to the speakers to power them. You'll also need to run a power cable from the battery to the amp(s) at the back, and installing a capacitor makes this a tad easier. What the previous poster said about a capacitor is mostly true, if your sub hits really hard your headlights might dim at night / etc if your battery can't take an instantaneous jump in current. A cap will run you about 50-70 bucks for a great one and takes an extra 20 minutes on the install - definitely worth it. In my 02 v6, I have a 400 watt rms 4 channel amp for my speakers and a 400 watt rms monoblock amp powering my sub, both connected to a 1-Farad capacitor and I've had my car battery for over 6 years and it still pushes a perfect 12V (Optima Red-Top). You can do this in a weekend if you're good with wires, reading instructions, and have a good friend around for some of the work - you'll be removing most of the paneling in the car, especially if you want component tweeters, etc.
I've been researching doing the same thing, here's a link you might find uber-helpful. I was even planning on getting the same speakers as this guy whenever I get a new GT (whenever my v6 finally dies, not looking very likely). Mustang Audio Install
A good rule of thumb on the Cap is 1 Farad per 1000 watts RMS, from what I've heard. Best of luck on the install, the weekend was definitely worth 6 years and counting of audio bliss on my 1-hour commute.