If you're making a portable you probably need something to watch it on. (Unless you want to guess what's happening in the game, but I wouldn't advise that) Anyway, this forum is your "Hacking a pocket TV/screen" one-stop solution. Share your experiences and knowledge here.
It most likely has a digital only interface. The GP32 screen is the same kind of screen that's used in many Palm and PocketPC devices. That's why, if you have ever programmed for the GP32, you'll find out really fast that the X and Y axis are turned 90 degrees clockwise. That's because the screen was intended to be viewed portrait, not landscape.