In Darkbasic Discussion, there's a sticky called "Game programming kit for beginners" There's a huge list of other support software including 3D modellers, and 2D applications.
Quote: "1. Is this possible with DBP or does it only support certain types of games eg platform or FPS?"
You can make pretty much anything, but if you decide on something big (like me), be prepared to spend a good decade or two making it. I'm only half joking.
Quote: "2. what modelling programs?"
No-one can tell you what modelling program to use. Try them all before making a decision. They all have free demos available to download.
Quote: "3. can you make your own sound effects to use in games?"
Yep. I've never gone into sound effects before, but for music I use midi. I believe MP3 and WAV can be used with the sound commands though.
Quote: "4. Is it possible to create and use photo-realistic graphics?"
Photorealism usually means very, very high poly, with very, very high resolution textures. Besides that fact that each model will take years to make, DBP isn't capable of running more than a few tens of thousands worth of polys at a decent framerate.
Quote: "5. Are there any major things that are not possible when creating a game that would be possible with say C++ ?"
I don't know much at all about C++. It's supposed to be hard. DB/P is really easy to use, and you can get pretty good results quite easily. It's still a programming language though, so it's never quite as simple as you'd like.