Welcome to the club Erick.S!
http://forums.altimas.org/zeromain thats the link you should bookmark!
All the info here is in its proper section (for the most part)... this type of discussion is usually in the "Suspension and wheels" Section....
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!)
The difference in the springs is if they are progressive rate or not, the eibach prokit is progressive, so it shouldnt wear on the shocks adversely.
If you are interested in a coilover, BC racing has just released their coilover kit for the AC.