i have clicking while turning and ROUGH vibration while driving, its worse as the speed increases. ive read it could be CV joint, or axles, or half shafts. which one do i need to fix both clicking and vibration?

also, would it be better to buy OEM from Nissan or go to autozone and get rebuilt ones and return my old ones for the core charge? how much is install usually?

Aftermarkets are just fine and a whole lot cheaper. Make sure they get you the right one. With or without a.b.s., 2.0 not 1.6. You can do axles yourself. From what I experienced on mine, when the outer joint is wore, it clicks. If the inner joint is wore, it vibrates. If it clicks from the right when you turn right it is the right axle. If noise from left on left, then left. If you don't know just have them both replaced. You can get hooked up for like $65 per axle. Cheap.

how do i know whether or not I have ABS? are the aftermarket ones ok for occasional racing and such?

so i need to tell them i need new AXLES? is the cv joint part of the axle?

Sounds like the CV joint, which can be purchased seperately from the axles themselves.
Here's a link to more information:
http://www.sr20deforum.com/showthread.php?s=&threadid=11278&highlight=raxles