Updating Photoshop 5.0 to 5.0.5 fails

Hi all,
Just built a new tower and am getting everthing loaded and configured. No issues thus far except that I have Adobe Photoshop 5.0, and have in the past with the same XP Home upgraded it to 5.0.5 . I have downloaded the zip file several times, unpacked it and attempted to run the exe. I get this:
Can't run 16 bit Windows program.
Cannot find file bla,bla,bla\SETUP.EXE(or one of it's components). Check to ensure the path and filename are correct and that all required libraries are available.
It does not matter where I uppack the zip to, so I don't think the first part of the message applies here. Any ideas would be appreciated. I have nothing running at when attempting to update, and have even shut down my security suite to no avail.

 

Thank You for the fix

Pete,
Thanks a lot. File name length was the culprit. When I moved the unzipped folder to the root drive it still wouldn't run, but the file name was long, so I changed it to simply PS which shortened the path to the EXE file enough and Voila!, it ran.