Attached Link: http://www.debevec.org/HDRShop/

As kaom says, you can use HDRShop for this. It's a good program for manipulating Low Dynamic Range (LDR) images as well as HDR - and is free (but is only for Windows unfortunately). 1.Start HDRShop and open your sky map (this must be 2 x height = width). Use the default settings for gamma etc. 2.Choose Image>Panorama>Panoramic Transformations. For the source image format on the left choose Latitude/Longitude. For the destination image choose Mirrored Ball. Change the pixel dimensions of the destination image to half width+height of your original. This should avoid too much interpolation. Click OK and then save the result as a LDR file. It should look something like there top image above. 3. Load your new image into Photoshop and use the clone tool to get rid of the two distorted areas. 4. Reverse the process in HDRShop. Load your new image, choose Panoramic Transformations. Choose Mirrored Ball for the source image and Latitude/Longitude for the destination image (same pixel dimensions as your original). Save the result as a LDR image, load into Carrara as a Background and enjoy! HTH Mark