400 error upon installing PHP

I can't quite figure out where I've gone wrong, but my PHP
installation isn't working.  I just installed PHP 5.3 (VC6) for
Windows on top of Apache 2.0.63, as CGI.  The apache part works fine
-- my browser can load .html files from apache's htdocs directory
without a problem.  But when I try to view a .php file I put into
htdocs (even if it's pure HTML), my browser returns a 400 error.

My apache httpd.conf file contains the following, which all looks
correct to me per the instructions:

#BEGIN PHP INSTALLER EDITS - REMOVE ONLY ON UNINSTALL
ScriptAlias /php/ "C:/Program Files/PHP/"
Action application/x-httpd-php "C:/Program Files/PHP/php-cgi.exe"
#END PHP INSTALLER EDITS - REMOVE ONLY ON UNINSTALL

So, where have I goofed?

thanks much,
Joshua