Hey,

There is a tutorial coming up on here in the next few days which will show you exactly how to work with polys and sub d's also as a bonus its car modeling.
But onto your problem you need to merge all the vertices to eachother around the light and front intake then when you convert to sub d's that will get rid of the curved edges, also hit 3 on your keypad while having the sub d object selected to bump up its display level job solved nice smooth car

although I suggest you check out the car tutorial will give you many tips to speed your workflow and make your car look better
Heres what the finsihed car looks like from the tutorial