Correct, some are just monitors with ins and outs, so you can plugs the PS2 into it and out with audio signals. Some are real nice with EVERYTHING built into it, which are nice also. Some are monitors with DVD/5.1 capabilities built-in (no CD/radio). They come in sizes ranging from 4.5"-7" in flip-outs too(from what I have seen for in-dash).

Its pretty simple to install too. I recently got a mag (can't remember the name atm) and it told you how to hook the PS2 to the car(underneath the glove-box), from start to finish. Looked nice by the end too.

Technically, you could just hook the PS2 to the monitor and for-go the rest and just have picture, although that would suck. The monitors are made just like your TV, minus the install(which can be a huge pain), it is almost plug-n-play.

Hope that helps