One of the most frustrating things about homebrew game development is that there’s almost an insurmountable amount of work that needs to be done just to get something decent to display on a screen. You can roll your own complete graphics and physics engines and still have nothing to show for it if there are no art assets to load.
QuantumG’s solution to the problem was to focus on developing the game engine using the model data from GTA3. Knowing that the art is already functional in another game allows you to focus on your code, and it’s more fun when you can see the immediate results of your work.
The blog entry walks you through his experience with extracting and using the mesh, texture, city, and character data and making use of it with the OGRE graphics engine. If you’ve ever played around with making a game before, but got discouraged for lack of art assets, this is really worth a read.