Shoutbox

I think there's a work around...same result virtually...
You can either use the current Playing status or make your own or not...and then do this;
Main Messenger Window > Preferences > Plus! > Preferences > Privacy Protection > Boss Protection > (choose a protection setting from 3 available) > Set a system wide shortcut > and set the status while hiding to your playing status...Click OK.
Now whenever you use that shortcut your status on MSN will automatically be set to playing and no toasts (popups as you called them) will be shown until you double click on the new icon on the taskbar). Or if you still want toasts to be shown, simply set your status to your playing status...
Hope this helps you