Quote - > Quote - It's actually a bit of a cheat.  I rendered the car by itself first and then pasted it onto the background image in paint shop pro.  The downside is that I'm not getting an accurate reflection map, but it does make it easier to put things in place.

How do you do to get the shadow then? I haven't found a way yet to get a shadow catcher with IDL.
And how do you do to get the EnvSphere reflection on the car while rendering only the car?

Are you using a light with ray-traced shadows enabled? If so, it shouldn't be a problem casting shadows using the ground plane as a shadow catcher, with or without IDL. 

As for the reflections - I just plug in an image map to those materials that are reflective.  Like I said, it's not really accurate but is usually passable.