How to change the table "user"?
 

If vbulletin uses the table "vb3_user", and phopost uses the table "user" How to force photopost to use the table "vb3_user"?

what are you trying to say here? In a standalone gallery our user table is pp_users.

If you are trying to install photopost to integrate with vbulletin then you would run the install and correctly install the application by answering all the asked for information. On step 4 of the install is a question called forum mysql table prefix. You would need to actually enter the correct table prefix for your forum there.

Photopost never looks for just user unless you have not placed the proper table prefix on the install. ;)

Did you resolve your issue? If you need anything else let me know.

Thank you! It was a theoretical question.

OH. ;) I was thinking you incorrectly installed the application and not understanding why you did not have a table prefix on the forum.