Windows Vista introduced a new imaging stack, called Windows Imaging Component (WIC), and uses it in Windows Explorer to create thumbnails for most image file formats.
Third-party software can use WIC codecs to support proprietary image formats such as Nikon NEF or Canon CR2 raw files, so that Windows Explorer shows thumbnails for these formats when the corresponding codec is installed. Microsoft maintains a page containing links to existing codecs.
Sadly, there is no publicly available codec for the Photoshop PSD format but the newly released Microsoft Expression Blend 3 design tool (which, by the way, is nothing short of amazing for WPF and Silverlight design) includes such a codec so installing Blend 3 automatically installs the PSD codec.
For those who don't have a need for Blend and don't want to install it, here is a little hacking guide to extract the codec (a 256KB dll) and use it separately:
Get the codec and its dependencies:
- Download Microsoft Expression Blend 3.0 (3.0.1927.0 7/20/2009) Trial: Link
- Open 'Blend_Trial_en.exe' from step (1) using a program like 7-Zip, and in the 'Setup' subfolder, open 'BlImp.cab' then extract 'PSDCodec.dll'
- Download the Visual C++ 2008 SP1 Redistributable Package (x86).
- Install the VC++ Runtime by running vcredist_x86.exe from step (3) above.
- Copy PSDCodec.dll from step (2) to some location on the harddisk, e.g. "C:\Program Files\PSDCodec"
- Register the codec from an administrator's command prompt by running the following command: regsvr32 "C:\Program Files\PSDCodec\PSDCodec.dll"
That's it, Windows Vista Explorer should soon begin to display thumbnails for all PSD files that were saved from Photoshop with the "Maximum Compatibility" option.
As a side effect, WIC-aware image viewers such as FastPictureViewer Professional automatically benefit from the codec installation and uses it to open and display the same PSD files with full fidelity.
Update: Interestingly enough, new versions of FastPictureViewer ship with their own codecs that Windows Explorer will pick up automatically so that PSD files and other image formats not natively supported by Explorer are displayed in the file manager after installation.
A free alternative that you may use is Pictus. It has not been updated for a long while, but it integrates PSD support in Windows Explorer even on newer versions of Windows provided that you make sure the option is checked during installation.
Last but not least, there is the free SageThumbs which does the very same thing.