Our primary domain uses SSL with no problems. We dont use a self signed cert.
Our phpbb install at
http://www.domain.com/phpbb/ "inherits" the SSL of the domain and can be accessed via http or https.
The only thing that doesnt work are the images. We don't get our company logo, and none of the theme images. We are using prosilver.
I'm sure it has to do with the logo being input as http instead of https, and we can fix that ourselves. We dont know what to do about all the theme images though.