Take a look at these articles -
How to create your own vBulletin-powered page! (uses vB templates) or
[How-To] vBulletin API Basics: Creating Custom Pages & Misc. - they will get you the basic page. Then, inside that page, you will want to grab the query that showthreads has to get all the posts in a thread given the threadid that is passed. Then, create a new template to use instead of the postbit template that spits out only the name, avatar, and message content and use it instead of the postbit.