Originally Posted by England
One difference is that PP can work as a stand alone product or in tune with vBulletin, and vbGallery requires you to have vBulletin forum software installed as it will not work alone.
I don't know how much vbGallery is but it should be the cheaper option mainly as it needs to work with the forum software.
Yep, that is indeed the biggest difference. PP Pro acts as it's own application that is capable of using your forums user DB & styling while PP vBGallery is an add-on specifically for vBulletin.
There are also feature differences such as PP Pro handling media files 'out-of-the-box' while PP vBGallery does not handle media files and relies upon a template hack to display them inline.