1. You would need to use the vb impex script to import Photopost users into vbulletin.
2. You would need to clear the usergroups table in photopost pp_usergroups mysql table.
3. Reinstall Photopost using all the old database settings etc so your data is still there but reinstall and integrate with vb3
4. run this script to realign photos and comments to the new userid's your users will have since you had to import Photopost users into vb.