Hi jwack: I’m using S2Member for my membership plugin, and it takes over BP reggie and sign up files in its own way, so I hesitate to respond from my own knowledge. But, I found this video http://wordpress.tv/2010/07/10/sabin-wilson-buddypress-boulder10/ by Lisa Sabin-Wilson that may be helpful for you, in understanding the page structure.
I’m reading her BuddyPress for Dummies now, but I just started and so am still, basically, a dummy;-)
