I downloaded one, and now I’m not entirely sure how to use it in the Lights menu.
Material -> Modifiers -> at the bottom over the “Channel discriptors” button
You need to use a landscape proportioned panorama - a spherical or cross image will not work. The HDRShop program will convert between formats (if it’s still available).
- Import the image into the Texture palette.
- Click the image thumbnail in the Light>Background sub-palette and select the image from the pop-up.
There’s more information here:
http://www.pixologic.com/docs/index.php/Background