Can't AddType .htm

I run Linux, Apache and PHP4.06. I want PHP to parse .htm documents. I have done this before on other servers with no problem by editing the following line in my httpd.conf. AddType application/x-httpd-php .htm .php .php4 .php3 But after restarting it doesn't do anything. .php files still work and .htm files don't work. If I try other suffixes other than .htm say ".dog" for example that works. So it seems something elsewhere is over riding it. Anyone got any suggestions. Regards Dan