I set up a free board at http://www.groupboard.com/demo/gbregister.shtml
I inserted Mori's Code Wrapper gadget in the page: Insert, More gadgets, search for Code Wrapper.
(Mori's Code Wrapper gadget may no longer be available but the Embed Gadget also works.)
I set it to 100% wide and 1200 pixels high and inserted the code generated on the groupboard site.
On a sub page I inserted the admin code they sent to me in an email after I registered.