MyBB Community Forums

Hello everyone. I am new to mybb, and in the early stages of planning some websites.
The websites will each have a blog, forum and webstore. The content will be slightly related, but different enough that I believe separate websites makes a lot of sense.
My question is this: Because the subject matter will be somewhat similar, I expect some crossover... I it possible to have two forums on two different websites... But only require a user to register for one?
Meaning that when a user registered for the forum on website A, they err automatically registered for the forum in website B?

You could use one database for both sites. Just edit your config.php file and be sure to enter the same database credentials. So basically both sites will be using one database, any changes to one site will be effect the second website with the very same changes.