bbPress.org

I am currently attempting something similar. I have an integrated WP and bbPress but want to switch to WPMU. I’ve successfully imported the user tables through phpMyAdmin. There are three columns you need to add to the wp_users table:

display_name - varchar(250) - blank default value

spam - tinyint(2) - default value = 0

deleted - tinyint(2) - default value = 0

And in wp_usermeta table you need to do a SQL search and replace to change all values that have wp_ to wp_1_ (because the main blog in WPMU has got that table prefix)

UPDATE wp_posts SET meta_key = replace(meta_key, 'wp_','wp_1_');