I explained above here what needs to be done to make the login work. There is no other way to change your cookie prefix other than running a query against the database. Now every host I know of has phpmyadmin in the site control panel. You can run this query possibly if your photopost is in the same database as
VB in the
VB admin query box.
UPDATE pp_settings SET setting='bb' WHERE id=172
You can hand edit config-int.php through ftp to turn on the overall vb3 integration and fill out the proper server paths and urls.
That should get you up and running with vb3 integration but to be able to login to admin you need to correct that cookie prefix.