The infamous white page is due to the fact that your php file is not configured properly. You installed your gallery within the forum directory. It has been specified that you need to install the gallery in the root directory of your domain. The first post f this thread is confusing. They state that you need to put the gallery in the root of your vbulletin and then go to say later that the root of your vbulletin is up a directory from the forum folder. If you wish to keep the setup you have now then I believe you need to add something here.
PHP Code:
$ret = GalleryEmbed::init(array('embedUri' => 'gallery.php',
'g2Uri' => 'http://www.mazdaoca.org/community/gallery/',
'loginRedirect' => 'index.php',
Your absolute paths are set up correctly, so you need to play with these figures here to get the corect value. I believe your embeduri is incorrect. But I can't say for sure. try putting the embeduri as ../gallery.php. I can't guarantee this will work this way. My suggestion to you would be to go back and install the gallery outside of the community folder. Look at my last post and follow it verbatim. I can guarantee that the way I have it set up will work because I have it set up that way. Or I can at least vouch. At any rate, the white page means that the code that I just quoted above has incorrect values. If you want to play with it then play with those figures.
As for your other question, sorry I didn't understand what you were asking the first time, but yeah, I have two db's one for the vbulletin and one for gallery. They are linked through the gallery2.php file.