This is really a new question isn't it?
In that plugin there is a line:
chat_world = "hellmoo_Chat"
So for that to work you need to have made another world called "hellmoo_Chat" and set its IP address to 0.0.0.0.
However that plugin is 10 years old. There are more recent ones that redirect to a miniwindow, which saves you having to have new worlds open. I think this is the latest thread about it:
http://www.gammon.com.au/forum/?id=12855
You would however need to adjust the triggers in it to match what comes from your MUD. The page you linked has some example triggers, and the page I mention above says:
--[[
Call this plugin by making as many triggers as you want in your main
world file (or other plugins) and then passing the style runs to this
plugin like this:
--]]
function chattrigger (name, line, wildcards, styles)
require "serialize"
check (CallPlugin ("10778718503f0c91106745f5",
"display", serialize.save_simple (styles)))
end -- chattrigger
So you basically use the triggers from your page, but change them to call the script above and it should work. In fact if you rename that function "chattrigger" to "redirect" then the work should be minimal.