ZMODELER!
(SA SUPPORT FOR .DFF not supported in free version!)
Ya If you want to have some simple fun with it try Textures. Open up the "gta3.img" file with IMG program and export the image you want and edit it with photoshop or MS paint etc.
just ask me about texture if you want to know. I'm an expert at textures. Not modeling though. If you after that ask someone else.