Forums Scripts & Popups Particular Channel in Focus

You can issue a "/join -n #".
If the channel window wasn't created as yet (e.g. first connect), the chan will be joined in a minimized window (thus not stealing focus). And if the channel window was already open (e.g. after a a reconnect - requires "keep channels open" ticked in Options:IRC), mIRC won't switch the focus to that window either in the rejoin. Finally, the favorites have a "minimized join" checkbox (Alt-J:Edit) which does the same as the -n switch.