To make Apache send any extension to the PHP interpreter, you need to modify the AddType handler. For example:
AddType application/x-httpd-php .php .php3 .phtml .html
Will make Apache parse .php .php3 .phtml and .html extensions as PHP documents. One word of caution.... although fast, parsing and outputing PHP still is much slower than sending out plain old html. If you add the .html extension, every .html page will go to the PHP interpreter regardless of whether it actually has PHP code or not. If you've only got 1 or 2 .html files with PHP code, from a performance point of view it would be better to rename them to .php. HTH,
Cheers,
Geoff A. Virgo