From this page:
the "Create a Synth" button opens a new window with this URL:http://cdn.photosynth.net/installer/PhotosynthInstall_21103171042.exe
and give the error:
404 - File or directory not found.
The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.
The button is actually labeled "Install Photosynth".
Clayton, it seems to be working for me now. Could you please retry?
Also reported here:
Apparently part of Photosynth's content distribution network was missing this file for a day or two.