Okay yeah the post above is confusing me a little
Let's see if we can explain how things work as far as the import is concerned.
Okay this is how things work. Photopost Pro would need to be integrated with vbulletin if you plan on importing vbgallery images etc. This is a given since vbgallery is a vbulletin addon. Now Photopost Pro though is not suspect to the same issues vbgallery has when vbulletin changes something as seen with the recent 3.6. Since we use our own language and template system we are 100% compatible with vbulletin 3.6 however vbgallery is not.
Therefore through this whole process you would integrate photopost with vbulletin. Now you could install Photopost as a standalone and import the vbgallery cats images etc however that still leaves you with one problem which is why you cant do it. You need to write a script to import vbulletin users into photopost users table. If you know how to write scripts you could totally separate things but there is no backwards user import feature anywhere here since users want to integrate with vb not separate from it.