Unfortunately, it isn't as easy as you're hoping. If you're interested in the artistic side of game development, you're going ot need to spend a good amount of time learning 3D modelling and animation, especially if you want to achieve some of the amazing graphics that are a hallmark of today's AAA game titles.
My suggestions for 3D modelling tools:
GMax (Basically 3DS Max, but free, though it isn't as extensive)
Blender 3D (free - http://www.blender3d.org)
Granted, I'm not very artistically inclined, so beyond giving some suggestions for modelling tools to use, I won't be of much help.
Have you consider using Google Sketch? There are many models available for you to play with. Grab a model (one that is license free), export it to some usable format, and 'play' further in your modeler of choice. Also, have you consider just using primitives for now?
i.e. Does the tank in your game need to be a fully modeled object? perhaps a flat rectangle can serve for now while you are working on the game mechanics. When you have something playable, you can swap out and use some nice models.
Good way to attract designers as well (ie the playable), because no one will make you models for a game that 'might be made'
There are also many low-cost low-polygon model packs out there.
Start by sketching, a stage that is overlooked by many designers starting out think things have to be done on a computer, go to the stationary store and get some pencils and a 500 pack of printer paper, and start sketching, and throwing away bits of paper.