Bob, since storage and duplication of files is cheap (only a few), one could create a "browse site" customized for each of the 3 first pages. --a directory dedicated to each of the first 3 pages, with an accompanying set of pages to browse. Each "sub site" would contain the browsing user until they click on a link to signup/register. The signup link could then contain the info needed to track which set the browser is coming from.
Just a thought... let me know if my description is unclear..