The solution is very simple and takes less than a minute to implement. You don’t need to even reboot Windows. The change is immediate.

    Download the file, photoshop_thumbnails.zip (62kb)
    Copy psicon.dll to C:\Program Files\Common Files\Adobe\Shell – if this folder doesn’t exist create it, for 64bit users: C:\Program Files (x86)\Common Files\Adobe\Shell\CS4
    Run Adobe.reg
    You now can view PSD files in Thumbnails view within Windows Explorer.