I don't see where the guide is on the site, but the guide is wrong if it tells you to use different ports in mIRC and in the router.
Whatever port range you setup in mIRC has to be the exact same port range you setup in your router.
For example, if you want to use 1024-1036 in mIRC, you need to forward 1024-1036 in the router. If you want 10051-10070, forward those. Basically it has to match up. This is likely why your setup wasn't working.