Forums mIRC Help Hide status window

If you mean the Status Window (as in the window that displays all your data for a given connection) then the command to hide it is /window -h "Status Window" and to show it again use /window -w "Status Window".

If you mean the Treebar (the window on the left of the main mIRC window which lists all windows that are open) then go to View in the menubar and untick the Treebar item.