Hi to all.
To Paul and tom322, thank you for your replies.
So if you have your forums under "forums" folder for example, just point sub-domain to that folder, change $main_url setting in setup_options.php (and probably other domain options the add-ons like Captcha may have), and also update .htaccess if you have special domain-related rules.
Paul's solution is elegant and straightforward because it does not involve moving of any files. Sadly, however, my situation may need a different solution - please see explanation below.
I may need to install WordPress in the root directory (example.com/). As I do not know what impact this would have on my miniBB forum in example.com/forums/, so I came up with the idea of moving it to a sub-domain - away from WordPress files. In other words, the plan is to set things up like so:
move from server path
(WordPress site will sit in /user/example.com/)
Hope this makes sense.
It is entirely possible that my 'disaster planning' is illogical and flawed. Perhaps someone with experience in running WordPress and miniBB will say: "Idiot! Installing WordPress in your site's root directory will not affect your existing forum located in the subdirectory /forums/ in any way: your forum will continue to run as it always has." (Wouldn't that be nice! :-))
I welcome and appreciate any advice/help you are happy to offer.
All best -