I am assuming vbgallery does not exist on site a so essentially all your doing is moving and upgrading vbgallery which is not that hard I would think. I can not say for sure as I have never tried it. I do not know what other database changes may or may not be done to vb.
1. move the vbgallery database tables over to the new server along with the vbgallery directory of files.
2. download vbgallery 3.0 and upload all the files to the new server to your gallery you transferred and the forums directory on site a so it has all the new vbgallery files.
3. Run the vbgallery install file and select upgrade to upgrade everything. You can then when done go to your vbgallery settings to the new server paths urls etc
worth trying I guess