htaccess file question

You'd have to experiment. Each web host provider decides how much you can change with your .htaccess files. Some allow more than others. But you might try something like this:

RedirectMatch foo.html foo.php

See the "redirect" directives here (for Apache 1.xx):
http://httpd.apache.org/docs/1.3/mod/mod_alias.html

Or here (for Apache 2.xx):
http://httpd.apache.org/docs/2.0/mod/mod_alias.html#redirect

And a google search for "apache redirect" will have lots of tutorials as well:
http://www.google.com/search?q=apache+redirect

Hope that helps! :)