NJ COUPES FTW!
Welcome to the club!
http://forums.altimas.org/zeromain thats the link you should bookmark!
All the info here is in its proper section (for the most part)...
The search button works too, and we are always here to help you out! (just try and post in the right section if you can, if you arent sure, dont worry theres no beatings issued!)
I went to HS in manalapan...
Anyways, you can get pretty much everything aftermarket... what were you looking to replace?
The only thing I cant see you being able to add is steering wheel controls (if it doesnt have it) or heated seats... ohh and a sunroof...
Everything else is able to be done in the aftermarket.