There are so many differing views across IRCds across what admin/owner/founder/etc. are the it'd be very difficult for mIRC to support events so that each one corresponded correctly to each IRCd's own definition.
isfounder/isadmin can be checked using $nick(
channel, nick, mode-prefix). I'm fairly certain this works, I'm sure I've used it in the past, but I honestly couldn't find a server with the appropriate non-standard modes to test it with. Which just goes to show that they're not all that popular really.
(de)founder/(de)admin events can be created using on rawmode and signals. I posted
something to more or less do that on the scripting forum once before. You coul simply use that code as is, or you could edit/extend it so it checks the network or IRCd in use and creates fullblown (de)founder/(de)admin signals.
