For HDRI create a giant sphere, well larger then your car.

Assign the sphere a lambert shader.

Assign your HDRI image for the Incandescence and Color.(Maya will not recognize the image but Mental Ray will and you will most likely need to rotate the image i did 90 degrees.)

Create a spot light and turn Intensity to 0(This causes maya not to use the default lighting and rely strictly off the HDRI sphere.)

Adjust the Ambient Color for intensity of HDRI.

Turn on Final Gathering

Render away
***To remove the HDRI image from the background, place it on its own render layer and turn of the render. It will render the lighting and reflections but not in the background.

Here's a sample pic: