what's up? welcome to PH. you should trade your G20 for her prelude. that's what you should do.
anyway, how much are you willing to spend on the prelude? for intake there's AEM, there's iceman. most would tell you to get the AEM which cost $200 roughly. others do custom intakes, which cost less than an AEM. for header, the most popular one for preludes is a 4-2-1 design by DC sports. mugen also makes one for preludes, but it's pretty expensive. the DC sports should do you fine if you choose to get an aftermarket header. some would suggest you stick with your factory header. you won't get a significant gain on your 00 lude with changing the header. a number of companies make cat-backs for prelude. popular ones include the apexi n1, greddy evo, racing medallion, and thermal research. myself, i have the n1 which looks good, decent increase in the high end, although it is pretty loud. any of these mods are easy to install bolt-ons which you can do yourself in your driveway to save some cash. from the manufacturer you'll pay about a grand for all of these. and can expect about a 15 hp gain from all three mods. hope this helps some. i'm sure others will chip in their thoughts.