Bad news bro, the A6.20 version is warez (crap, downloaded free online, illegal)...
...But back to the topic, alot of people come here wanting to make a GTA type game. In fact, everyone that doesn't even do this sh*t does, but it's not quite that easy. however, it can be done, it just takes alot of time and work, creating a huge city piece by piece. Then you have speed issues because there's too much stuff, then you need to optimize, bla bla bla, and you later give up on it

I recommend starting with a simple FPS to get the feel of things, and make sure your really into game dev, because as you'll learn (if you get a running copy of 3D GGameStudio), it's a major pain in the ass...