Dark Giratina, for the program I would recommend RPG Maker XP (quite simple to use). If you want to create a PMD game, then you have to search for the tileset, because I am quite sure I haven't seen any of those.
Dark Giratina, I don't know the exact people making PMD games, but if you search or browse through other forums, you should be able to find some information regarding the game.
The main character from Portal is a girl, and the guy in my avy's wearing a fedora for pete's sake. Plus there's rain and cars, neither or which you see in Portal.