"I'm not sure how to add your own to that..."
You need to add the network to the server list in mIRC options:
ALT+O > Connect > Servers
Under the drop down list click on 'Add'. Fill in the details where necessary - the 'Group:' parameter is the part that is added to the list. Once added this Group should now show up in the network list of the Perform section, and in the network list of Favourites.
You can also do it through the command line with (primarily) the -a switch of /server, see /help /server.
Regards,
