I already searched for a game car tutorial (not to much polygons), but all i came up with are overdetailed cars or to less detailed once(as modelling tutorials).
I really dont know how much polygons are good for a gaming car and maybe the one or the other in here, knows of a good tutorial?
Celofa
here i think this tut may help: http://darkscarab.com/resources/tutorials.php?id=43 if you think there are to many just start "cutting corners" :) it was made for blender but you can easily use it if u use 3d studio or maya
hope this helps
polycount will depend on the function of the car, is it a playable item or just decoration? more polys the former and less the latter. if you think of it in terms of a playable character the you can go quite high, literally 4000 polys (8000 tris). cars can be quite fun and if you have a basic knowledge of modeling and topology you'll not need a tutorial. start at the wheel arches though as it'll make the rest a hell of a lot easier. get some good image planes (google car blue prints) front, side and top at the very least and honestly you'll be wondering why you wanted a tutorial in the first place. if you really do want some help then leave a comment and i'll do what i can. good luck and just have fun with it.