Just "intersect with model" as Gaieus says again for the other side...it worked fine for me.
I had a look at your model...its looking pretty good so far. If you use more components, your modeling will speed up significantly. For example, each headlight should be a component(and would look better if it was smoothed and the circle it was constructed from had more segments). If each of the vertical bars on the grill was a component, you could copy an array to space them perfectly. Maybe you would have a hard time modeling this way, but if you split the model in half the long way, make it a component, copy/flip to the other side, then you only have to model half as much because whatever you do to one side automatically happens to the other side.
Like this:
[image: dQby_petehood05.jpg]
[image: Ft8Y_petehood051.jpg]
[image: rNJL_petehood052.jpg]
There are a lot of tricks to help you to model faster - have a look at these tutorials if you haven't already: http://sketchup.google.com/training/videos/familiar_with_gsu.html An hour invested here will save you countless hours and headaches down the road! I hope this helps, cheers!