About a contest you are free to modify your code however you choose if it does not work how you want.
You must have vbulletin first to integrate Photopos. There is a way to add one later but it requires alot of work and changes which is not for the starter. vbgallery is a lite gallery with not all the features of Photopost that only works with vbulletin. Here is a comparison.
http://www.photopost.com/compare.html