I don't think the quality is that bad considering the resolution is 1280x960. Sometimes sharp/crisp edges and hi-res aren't helping especially if the model is a low poly object...
However, the roof seems to be translucent.
'The model is OK' because it is small in your render. You have 2 cars fitted in a 1024x512 which means approx 530x328 for 1 car.
What I meant was that is no need to go the extra resolutions for a low res model. It would not help the image, it would only show up all the pointy edges caused by the low res poly. For example on Bose's image there http://www.lfsforum.net/attach ... id=78124&d=1234632402 (sorry Bose, I am not saying it is a bad render) But it just 'magnify' the low poly bits in detail.