I followed the installation notes for PHP4 beta 2 in your readme.txt file, which came along with the DLLs.

- Install the php.ini file and the DLLs as mentioned above.
- Start the Microsoft Management Console (may appear as
  'Internet Service Manager').
- Under 'ISAPI Filters', add a new ISAPI filter.  Use 'PHP' as the filter name,
  and supply a path to the php4isapi.dll that is included in the distribution.
- Under 'Home Directory', click on the 'Configuration' button.  Add a new entry
  to the Application Mappings;  Use the path the php4isapi.dll as the Executable,
  supply .php as the extension, leave 'Method exclusions', blank, and check
  the Script engine checkbox.
- Stop IIS completely (you would have to stop the IIS Administration service for
  that - stopping it through the Management Console isn't good enough;  You can
  do it by typing 'net stop iisadmin' on a command prompt).
- Start IIS again (you can do it by typing 'net start w3svc' on a command prompt).

BOOM! Dr. Watson says there is an application error.
the console says System Error 1067
IIS fails to fire up.

So I never got to
- Put a .php file under your Web server's document root and check if it works!

I used the original PHP.INI file