Making Simple Backgrounds
Setting up a background in Max can be a frustrating experience. The way I will describe here does not require a lot of work. This is how I do mine.
1.) Have your vehicles height, width and length close at hand.
2.) In the top viewport make a single segmented plane with the length and width measurements.
3.) Make a new material with your background bitmap(s) as part of it. If you have 3 different bitmaps make them sub-materials.
4.) Map the top view background to this plane in the top viewport. If you have just one background image, you'll have to use the "UV Unwrap" modifier and crop to the area of the bitmap you want showing on the plane. Collapse the modifier stack.
5.) Move the plane down below the area where there will actually be parts. Think of it as the ground and you will be working all above the ground.
6.) In the planes properties, uncheck "Show Frozen in Grey" and check the "Freeze" box.
7.) Make another plane using the lenght and height dimensions in the left viewport. (This assumes your side image is of the left side of the vehicle.)
8.) Map the side background image to this plane.
9.) Move it off to the side like it is a wall to the right of your work area.
10.) Repeat step 6 for this plane.
11.) In the back viewport make a plane with the height and width dimensions.
12.) Map the front view background to this plane.
13.) Again, move it so it is like a back wall of your work area.
14.) Repeat step 6 for this plane.

When you are done, you should have at least a 3 sided box. You could have more if you have more than 3 views.

Now if you make your part that your working on, "See Through" in it properties box, you can see the background thru your part.