This tutorial describes how to use panoramas created by SkyPaint as backgrounds in 3DStudio MAX R2. Requirements:
Open up the 3DStudio MAX material editor by pressing on this icon: 
Press the 'get material' icon: 
A list of material types will appear. Choose 'Reflect/Refract', and press Ok.
Back in the material editor, you will see a list of Reflect/Refract Parameters. Make sure the 'From File' and 'Use Environment Map' check-boxes are checked.
In the 'From File' section of the parameters, click on the "Up" button. The standard file browser will come up; select the _UP.tga file that SkyPaint created. For example, if you saved a panorama named 'Day', click on the Up button and then choose the 'Day_UP.tga' file.
3DStudio will then automatically fill in the Down/Left/Right/Front/Back buttons with the other 5 images that make up the panorama, and will display the panorama in the material preview.
Give the material a descriptive name (type it into the box next to the
"Type:Reflect/Refract" button) so it is easier to find in material
lists.
Choose 'Environment' from the 'Rendering' pull-down menu:
When the Environment dialog box comes up, drag the material from the Material Editor and drop it onto the 'Environment Map' button. The panorama is assigned and will be used as the background when the scene is rendered.
The panorama will not be displayed until you render your scene. Do a quick test render by selecting the Perspective viewport and doing a test render. This is what the result looks like, using an elephant model and a low-resolution sunset panorama:
See the 3DStudio MAX 2 documentation for more information on background environment maps. Also see the Learning 3D Studio MAX tutorial "Working with Backgrounds", available at http://www.ktx.com/3dsmaxr2/html/new_tutorials_1.html.