Ray,
Existing members will be transferred over together with their passwords and emails but not their avatars as I understand it. Not sure what other info will come across but settings will be different in the new forum so preferences will probablyy have to be reset. All the posts together with images in posts should transfer but not albums at this stage. Whether your albums will be converted into a personal gallery is very uncertain.
I'm hoping for more info early in the week.
There is supposed to be a general information FAQ topic which will help people get used to the new setup.
I will ask Martin if I can set up a topic on Mayhem where anyone who gets stuck can contact me.
Colin