I do not know. Ziria is the first game, and the entire system was made entirely for the purpose of that game itself. The fourth game is a Saturn game, and should be played via the Saturn, for full enjoyment, I don't know how a person could in take that in on a PSP, it is not the same.
Zero itself should have been made for the PCE, the SNES had some good things about it, but it just blows Dragon Quest away and that is about it. Every stage in Zero is like, find the missing item, go foward, fight area master, get power up, and that is it. The story itself is really intresting but I think RED/Hudson reused portions of
III/IV inside of it. The intresting thing in Zero is the summon system, and the egg/time system. Which affects how everything looks, and reacts to how long you spend playing this game, like Pokemon GS. I never finished the game, I got tired of the ultimate RPGness of the game itself.