I guess you had some kind of rewrite or defined gforum.cgi as index file in the "old version".
Nevertheless as far as I can see there is a mistake. I used to start at

http://www.gossamer-threads.com/perl/gforum/ which still shows the index page of the forum but you cannot go anywhere because there is 404

I do have seen that it works with http://www.gossamer-threads.com/perl/gforum/gforum.cgi

But I do like the first impression of the redesign of your site

n || i || k || o

Thanks, looks like it's a bad rewrite rule. I'll get Alex to fix that up later.

Adrian