You are all making it way too difficult. Just install the following codecs which supports nearly every RAW file under the sun including DNG; 32 and 64bit and works under Windows 7:
Fast Picture Viewer | WIC RAW Codec Pack for Windows 7, Vista and XP
The codecs are free but the viewer isn't but you only want to view the thumbnails so you don't need the viewer. When you install, be selective as to which codecs you want to install as it supports all makes.
As for PSD files: this was supported by older versions of Photoshop but CS4 does not include the required dll anymore. Some had luck restoring the dll from an older version of Photoshop but I couldn't get that to work. I did manage to display thumbnails of PSD's under Windows 7 but for the life of me can't remember off the top of my head how I did it. I'd have to look it up if anybody wants this functionality. I probably have notes somewhere.