A .5 farad for 600watt RMS, or 1.0 Farad for 1000w rms capacitor would help a lot in making your car's battery last longer as well.
http://www.northsideelectronics.com/.../17-1FCAPM.gif

I have about 950 watts running in my Z and I don't have any problems with dimming or battery draining.

250.1:
1 Sub @ 2ohms = 500w RMS

600a4:
Front Focals VRS @4ohms = 75w RMSx2 150w
Stock Rears @ 2ohms 150w RMSx2 = 300w

DO NOT USE A CAP

I can link you to sooo many websites about how they are bad and just a band aid to a bigger problem. If you need one of those to stop dimming or what not you need to upgrade your alternator.

From everyone's advice I'm thinking about going with this setup:

Focal Access 165A1
IDQ12V2.D4 - Image Dynamics 12" IDQ Dual 4 Ohm Subwoofer

Not sure on amp though, preference anyone? They're both the same price and similar rating.
G4500 - JL Audio 4 Ch 1000 Watt Amplifier
MRP-F600 - Alpine V-Power Series 4-channel 600 Watt Amplifier

I like alpine but JL amps are good as well you can go either one.

And how many feet of speaker wiring will I need for my setup? Most likely I'll be placing the amp under the seat.

Well you are only going to really need it for the sub and to the fronts. So around 25ft of 14 gauge and maybe 12ft or 10 gauge for the sub.

You can use the factory speaker wire in the doors IF YOU WANT but you will get better power threw a new piece going to the new speakers.

thanks!

what gauge wiring are the stock do you know? how hard was it to run the new wiring into the door? i don't think it's that bad i haven't taken a close look at it yet. and how long RCA cables do you recommend? 12ft? 17ft?

Well the new wire you will have to drill a hole threw the door harness to run the new wire threw the factory wire is like 18 gauge. Just remember to run a new piece to the new tweeter.

And the one peice of advice killed five small children in a third world country. :(

I've always wanted to run aftermarket speaker wire to all my speakers, I'm sure I would be able to tell the difference.

Also, please type through Big, not threw, JEEZ. lol <3

???

Definitly DONT waste your money on a cap! Caps are a bandaid solution at best. The 370Z has a very hefty alternator, Its 150AMPS!! the largest I have ever seen in a compact car. You can exceed 1000watts rms but you really should get a Stinger or Oddyesse Dry cell battery if you want any kind of life out of the battery if you are pushing this kind of power.

The battery is the only weak link here in the 370Z.

I know Big A is not a big JL Audio fan and thats ok, but I think JL is a great option with your budget. The G series amps by JL are a great value and are excellent amplifiers for the money.

I think the IDQ12 is a great sub and 250 watts is PLENTY! of power. This sub is pretty legendary and it will make you one happy camper! The Alpine MRP amps are very reliable but not the most dynamic amps. I think you would be happier with the JL G4500, its a better amp! However, Alpine PDX 4.100 would be even better and its more efficient! However, add another $100.00 to the budget.

Here is another tip that will save you some cash. For amp wire, go to a Welding shop and buy some 4 or 2 GA Welding Cable! Its premium grade with the small strands and its pure OFC Copper and its half the price of Car Audio wire. (Most Car Audio wire nowdays is Copper Coated Aluminum)

BTW, If you were happy with the stock system in your Lexus, this system is going to Rape your ears!

I honestly do not want to get into a war about this. I use to swear by caps and all back in the day. Than I found out somethings about them and all. Yes they do help take some load off the electrical system. But if you do need a cap you would be better off getting a new alternator or a second battery. Like I said people have there opinions. So let's agree to disagree.