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