By default, you can install vBulletin to utilize all https URLs. However, this does not mean that upon viewing your website or typing your domain into the address bar on a clients web browser, you will be forced to a secure connection. In fact, that first page will be insecure, and only the next page they navigate to and further will be secured by SSL.

What you need to do is add something like this to your .htaccess file that is located in the root directory of your vBulletin installation.

Code:
RewriteEngine On 
RewriteCond %{SERVER_PORT} 80
RewriteCond %{HTTP_HOST} ^overclockedlan\.pro$ [OR]
RewriteCond %{HTTP_HOST} ^www\.overclockedlan\.pro$
RewriteRule ^(.*)$ https://overclockedlan.pro/$1 [R,L]
Obviously, you want to replaced "overclockedlan" and ".pro" with your domains information. The "https://" should remain left alone.
You should already have an active, installed SSL certificate before you attempt to do this, as it will cause your browser to go haywire.

Upon success, when first visiting your website by typing the domain in your address bar without https://

e.g overclockedlan.pro

You should be presented with a secure, encrypted page provided there are no un-encrypted images on the page.
All images and embed codes should have http:// replaced in them to https:// to ensure maximum security across your website.
It looks good to your visitors, and it looks good to search engines.