the version i see available from the php.net download page:
either 5.3.8 or 5.2.17
I do not see a link for 5.1.17
in Going from 5.1 to 5.2, they stopped using the php-cgi.exe file and went to using the php5isapi.dll instead.
the guide i pointed you to is intended for the php version 5.2 instead of php version 5.1