MyBB Community Forums

Alright, so I am going to be using a MyBB forum in two places on my site--as the index and a community (on a sub-domain). The index won't be a normal MyBB board--it will be for articles, but this is not important. I want to have the two forums be separate in all bit two ways. I want there to be separate posts for board 1 (index) and board 2 (community). I wan everything to be separate for the boards except for user registration and logins. I figure I can edit the register code to add the registration to the other MySQL database pretty easily--just some code edits. I also want a user to be able to log on on either board 1 or board 2. This is where I come to one of my questions. If I set the cookie path for both to .mydomain.com would it log on to board 1 and board 2? 

My second question is about the members profiles. It would be nice if I could have somebody change something on thief board 2 profile--like their avatar--and have it change on board one. Is this possible?

If the cookie domain and path is the same then it will probably work yes. I don't really know as I haven't tried anything like that

For the second question if you are bridging the user login anyway you are technically bridging the users table too. Therefore you will be bridging the avatars. (As the avatars field is in the users table).