Creating a believable 3d model is strictly tied with an accurate definition of its materials and textures: realizing and correctly applying the textures on a model is a complex and long process in the creation of photorealistic renderings.
About the rendering process, i will simply descrive how to obtain a believable rendering in an exterior environment, and we will be greatly helped in this achievement by the new characteristics of the many global-illumination capable rendering engines.
Nowadays there are many rendering options to the average 3ds max user, from the built in "Light tracer" to 3rd party rendering engines (i.e. Splutterfish's Brazil, Chaotic Dimensions's Vray, Cebas's Final Render). To add even more, the latest 6th release of 3ds max made many artist's dream come true: the integration of Mental Ray 3.2.
The principles behind global illumination are common to all of this options, but interfaces and programmin algorythms differ quite a lot, bringing up confusion and differences in quaity and performance.
For the sake of simplicity i will discuss only the Light Tracer.
To complete this tutorial you will need 3ds max 5 (at least) and a graphic software like Macromedia Freehand or Fireworks (which was my choice), or Adobe Photshop or a similar software. I will not discuss the operations needed to paint in these softwares, but for our purposes we will just need a very basic understanding on how to create texts and shapes, so everybody reading this should be able to go through the process.
Section 1: Planning
Just as you plan ahead the number of faces your model will need for its purposes, in the same way you also have to plan the size of the textures you will realize. Finding yourself with wrong textures in the end is a very bad experience. In our project, we are aiming for *at least* 1024x768 detailed renderings: this means that all of our textures will have a minimum resolution. Lower reolutions will almost surely lead to artifacts in our final renders. To simplify, imagine you have a bonnet texture at 200x200 pixels: if you render an image where the bonnet fits the render, you won't be able to render images larger than 200x200 without getting artifacts, as 3ds max has to guess the missing informations. Nowadays hard disk space is (finally and luckily) a minor problem, so i always tend to "oversize" the textures so i am 100% sure they will meet my needs. In this case i went for 2000x2000 pixel textures for larger areas (as the bonnet) and 1000x1000 for smaller panels. The actions required to create the textures and to define UVW coordinates on the whole model are repetitive and fairly simple, hence i will explain how to apply textures and materials to a single element, the bonnet: it's up to you to continue with the rest ;)