There are three sprites being used: One sprite for the 'content' area, one for the vertical scrollbar and one for the left scrollbar.
The content area uses two behaviours: (1) The "ScrollingTarget.Images" behaviour which scrolls the content image in response to messages from the scrollbars, and (2) a 'PageLoader' behaviour which renders the page layout. The scrollbar sprites use the "GenericScrollBar_Horizonal" and "GenericScrollBar_Vertical " behaviours.
Each 'page' is a property list describing the page contents.There is a utility script called 'layoutmaker' to help automate the process of creating these property lists.
Currently using a property list to describe the page layout (each element is has properties such as rect, Ink, source member etc). If anyone feels like writing a HTML or XML parser, let us know.