Redirect in Apache

[Pankaj Halder]

I'm using Apache 2.2.10 (Unix), and want to redirect all the request of
http://mydoamin.com to http://www.mydomain.com

In my .htaccess, I added

RewriteBase /
RewriteCond %{HTTP_HOST} !^www.mydomain.com$ [NC]
RewriteRule ^(.*)$ http://www.mydomain.com/$1 [L,R=301]

But it does not work. Should I restart the server for the new .htaccess?

Or should I use httpd.conf instead of .htaccess?