One of the major features of FastPictureViewer Professional
(vs. Home Basic) is raw support. The program comes with its own raw codecs (same as those in the separate Codec Pack) and supports fast JPEG previewing for very
fast CR2 (and other raw formats) viewing.
The Codec Pack, on the other hand, adds support for 10 extra formats to FPV Pro, including Photoshop PSD, as well as EXIF-based JPEG auto-rotation for JPEG thumbnails and previews in Windows Vista and Windows 7 Explorer, so both products work well together.