You may not welcome this opinion, but if you want to go fast, why are you starting with an econobox?

Sorry,  I just don't understand the mindset of those who buy "sensible" Japanese cars and then want to try to turn them into something vaguely racy.      Wanna go fast?  Do the sensible thing, which is to buy a Z-28 or a Mustang.    You'll get a lot faster for a lot less money and not end up with an undersized,
super high-strung engine that's ready to explode at any time it actually delivers 300 HP or more.

It's a RICER, not a RACER.   BIG difference.


CJ

A five hundred dollar Nitrous kit should do the trick. If the cars engine is in decent shape at all a 75 shot wont do any real damage under moderate usage. You can spend a lot more money on parts that will either give you no real gains, or jeopordize reliability, and still not see nearly the increase in performance.

Cold Air intakes only make significant power on highly modded engines, same with exhaust. OF course you will find that just about every body who installs either will tell you that they "felt a big difference", the truth is that what they got was a percieved difference rather than a real difference. Butt dynos are notoriously inaccurate. Plus the extra sound from performance exhausts and CAIs is there all of the time, not just when you want a few extra horses.

Installing nitrous is not very difficult, especially if you buy one of the application specific kits. The kits will have every fastener and line you need as well as precise directions for your vehicle.

ETA: As tempting as those pictures may be, do not turn your car into anything starwars related, your wife will leave you, and ARFCOM will excomunicate you. The big wings, or as I sometimes call them, extra weight that adds drag and decreases trap times, are no good either.

New or old,  a Civic is an econobox, period.   Meaning,  you have to spend big bucks to get worthwhile gains in power out of it.  

Don't get me wrong,  I like Hondas, and Toyotas, and even Nissans.   But with the exception of the
models that are INTENDED to be very sporty right off the dealer's lot (Supra, for example),  
it's not worth it (in my opinion) to try to make them more than what they already are and that's not
particularly fast.

They're sensible, well-engineered cars that shouldn't cost much to operate and maintain.
Don't try to race them.   You will spend too much money on it only to get your ass handed to you
by someone with a dead stock 5.0 Mustang.

CJ