Have you found a free car model so you can look at it inside a modeling program? Then you could try making one that looks a little different next to the first one. That should give you enough practice that you could try making a fancier one from a drawing.

What modeling software do you want to use. Blender.org is good and free however the learning curve is steeper for a beginner. If cost is an issue I suggest Wings3d for modeling the cars mesh and get DAZ 3D Studio (DS) (free at daz3d.com) to rig it, and export as FBX for your game. DAZ also has decimator (poly reduction) and texture atlas (formats all material group & layers to one) plug ins to help make the figure the proper size and format for your game. Animations can be created in the DS timeline and exported as BHV. You may need a tool like Ultimate Unwrap 3D to help with file format conversions (.fbx to .x say) and UV layout and animation loading. If you have some cash to spare suggest Poser Pro Game Dev over DAZ because its a bit easier to learn and more flexible in terms of compatibility and such. Just this week I made this Peashooter airplane figure rigged for game action with Poser and ZBrush modeler. http://www.vanishingpoint.biz/productdetail.asp?productID=2754