installation folder/domain?

Hi,

I would like to learn which is the best method to house the membership plugin if we don’t install it on the main domain? It can be installed on a subdomain or on an independent installation of WP in a sub-directory under the main domain?

But how will then PMP will apply content restriction rules to the main site if it’s not installed there? (I am assuming that user accounts and session cookies are shared by both installations of the WP)