This "no input file" thread seems to be well spidered, but has a confusing mix of problem and solution statements.
In particular, one should distinguish between Win, Linux, Apache, and IIS, and CGI vs ISAPI scenarios -- which could have different causes.
My variant was Win 2000, PHP5, IIS5, ISAPI. First I verified that PHP was working from the command line:
If not, you have a PHP issue not related to the webserver you've selected. Fix that first. But I suspect if you are seeing "no input file", you've already got PHP mostly working.
Then I had to change the PHP.INI setting for
cgi_force_redirect = 0
as noted here http://us2.php.net/install.windows.
Unlike some of the postings here, I did not have a need to reboot the server, so long as IIS was restarted from the Services in Control Panel (the whole service, not just the site involved), nor did the doc_root setting, which was null, make any difference. You mileage could vary. Permissions problems could also be a cause.
Beware of caching when testing solutions.
Lastly, I am reminded how much time is saved by an all-in-one install as provided by http://devside.net if you have enough permissions to go that route. For Windows users, it's a big timesaver.
Good luck getting around this nuisance.