Move the imported images to form an approximation to the correct orthogonal views, all related together.
Then you can check they are all the same size so that similar places on each align - scale an image slightly as needed, or make adjustments in the modeling to suit...
Now start drawing edges that outline the main forms - there are tools like weld to make them curves and extrudeEdgesByRails etc... BUT you can make the 'profiles' and then 'stitch' it together by hand and adjust the forms as you go.
Make it out of manageable sized pieces [sub-groups/components etc].
Remember that a car is pretty much symmetrical so it quite easy to model one half of it as a component and copy and scale -1 the two halves together, so then changing one half alters the other one automatically...
This means you're not trying to make the two sides the same all of the time...
There are some good car tutorials out there - try this for a start...
http://www.youtube.com/watch?v=OlDxc2wyIhY&feature=related