I beleive my post above shows reviewpost needs to use photopost user database hense the two things you need to do after installing reviewpost
If you need more specific guide let me know. It should just be a matter of moving the users and setting the integration.
Here is 4 queries you can do in phpmyadmin after installing Photopost that would do the whole thing
DROP TABLE pp_users
RENAME TABLE rp_users TO pp_users
UPDATE rp_settings SET setting='photopost' WHERE id=41
UPDATE rp_settings SET setting='pp_' WHERE id=83