Neobud, thank you so much for your kind advice, I now have now have Usenet forums up and running at my site,
www.edinburghtalk.com.
It turned out that the problem was down to a mistake (or, rather, omission) in the readme.txt, obviously there's a fair amount of stuff that hasn't been updated.
Anyway, thanks again for taking the time to address my problem, and thanks to Lierduh for making this incredible extention available for vb3.5 - it's going to make a huge difference to users of sites like mine.
I am now concentrating on making this more usable, in particular I want to find a way to make the "remove Reply button, use Quote buttons instead" amendment more user friendly, possibly by using a different version of the Quote button in Usenet forum or, perhaps, a repeated reminder throughout such threads.