Membership and Paypal setup help

I have setup my membership plugin according to your install/setup instructions. User fills our their username/password, clicks the subcribe, pays at paypal, and then is just redirected back to the site home page. Their credit card is charged, the user account is created (but not activated) in wordpress (3.1 + Multisite+Buddypress). How do I setup paypal to link back to my wordpress to activate the user account and always keep their account updated (like change their membership if they cancel their paypal payment). I've searched over the forums for hours and can't find some sort of guide. Does one exist?