WPF ListBox with a ListBox - UI Virtualization and Scrolling

Question

My prototype displays \"documents\" that contain \"pages\" that are represented by thumbnail images. Each document can have any number of pages. For example, there might be

Answer 1

Please allow me to preface this answer with a question: Does the user have to see each and every thumbnail within every item in the list at all times?

If the answer to that question is 'no', then perhaps it would be feasible to limit the number of visible pages within the inner item template (given that you have indicated the scrolling works well with, say, 5 pages) and use a separate 'selected item' template that is larger and displays all pages for that document? Billy Hollis explains how to 'pop' a selected item out in a listbox on dnrtv episode 115