Like Grim said, you will need to modify the bulbs or the housings to make them fit. The Altima uses D2R bulbs and are only designed for reflector HID housings. I've done it before, just make sure you have a dremel or equivelant and random bits and cutoff wheels. Also, I would suggest re-wiring the headlights and use stronger relays because of the ballasts. Good luck.
Also, to get the complete HID setup, it will have the Bulbs, Ballasts, and ignitors. It's not like on Acura's, Mercedes, Audi's and what not where it is just the bulbs and ballasts.