PSD thumbnails?

Does anyone know if Extensis Portfolio displays PSD thumbnails?
Apparently, Windows XP does not. I downloaded Microsoft's RAW image
thumbnail viewer and that works great, but it sure would be good to be
able to see the thumbnails of PSD files as that is how I save my edited
and un-flattened image files. I only save as flattened TIFFs when I need
to send off a file to someone else for viewing or printing, as that lets
me know which files are for which purpose.

Thanks for any information.

David A.