Ah sorry, I should have said how to use it.

Press Alt+R, that will open mIRCs script editor.
Make sure you are on the "Remotes" tab.
Paste that into a new file (File menu / New) in the editor window, save it as <nameyouchoose>.mrc.
Close the editor. (Press OK)
Type
/remote on in the editbox of any mirc window. mIRC will say
* Remote is on (Ctcps,Events,Raw)Done, when someone mentions your nick in a channel and mIRC is not the active applcation a dialog will appear in the lower right corner of the desktop (above the task tray) with their nick and the message (if its too long it will be truncated) and mirc will beep, unless you set the soundfile as I suggested.
The default display of the message will not be affected in any way.
