Yeah, I think 2 was the easiest. 3 wasn't too bad but I played it on easy first, but I couldn't do the last bit too. 1 is the scariest >.<
Project Zero 1, 2, and 3 are on Playstation 2.
I think 1 was later released for Xbox. And 2 is released on Xbox and it is the Directors Cut edition, with extra stuff, and I bought that the other day.
The new one, Project Zero 4 is set to come out on the Nintendo Wii. There are rumours they are not releasing it on the other consoles, but that is yet to be confirmed.
Obviously, since you kill ghosts with the camera, the Nintendo Wii would be a good choice because you could hold the Wii mote up like a camera, and snap A or something to take the picture.
A really good website for more info about the game is here :
Beyond The Camera's Lens