Actually I want to make web pages with .html extension but still I want that they should be parsed by PHP parser. Is it possible??
Yes of course it's possible. I suggest you check this tutorial out: http://techtuts.com/?view=tutorials&act=tutorial&id=452
It might be a better strategy to use mod_rewrite for this purpose. That way you can detect if the html file exists first, if not it'll try to map it to a php file. I'd worry that there'd be slight slowdowns if every HTML file gets fed to the PHP interpreter instead of being served straight up by apache.
I think what sam1 wants to achieve is to have files with .html extension to be considered as PHP files. You'd probably want to use mod_rewrite if, for example, the files in the server have .php extension, and you want requests for index.html results in index.php being served. This would mean you'd get the same page if you request for index.html and index.php (both will work), unless of course there are other rewrite rules. Also, talking about slowdown, using mod_rewrite can of course also slow down server response.