We can achieve this using mod_rewrite which is already compiled into your Apache web server here at GlowHost.com
This will redirect any access to the non-secure site to the secure site at https://yourdomain.com
Make sure you have an SSL certificate for your domain!
Stick this in your .htaccess file:
RewriteEngine On
RewriteCond %{SERVER_PORT} !^443$
RewriteRule (.*) https://yourdomain.com/ [L]
If you want to simply redirect all requests for a certain directory, for example your shopping cart installation, you can do something like:
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/cart/.*
RewriteCond %{SERVER_PORT} !^443$
RewriteRule (.*) https://yourdomain.com/ [L]