whilst awaiting a reply i have since delved further into this issue myself. i have discovered the section of the user manual covering extensionless URLs.
However, initially i was confused as to what this mysterious page sf404.aspx
was, and where it resided (and then deciding i'd just supply IIS with the path to this page - whether it exists or not
so, after pointing IIS 404's at this non-existent file i seem to have garnered the desired effect of being able to use extensionless URLs for page groups.
however all is not as well as it sounds. the URL produced after using an extensionless URL is very unwieldly and long. For example typing in the URL:http://localhost/section/subsection/
results in the following URL:http://localhost/section/subsection/index.html?404;http://localhost:80/section/subsection
As can be seen, this URL is hardly desirable. it would be preferrable if the URL did not get altered when the redirect is performed.