If you take a look at the Alerts tab you will see exactly what you want.
You are able to search by Mode S, Registration, Range, Flight ID, Aircraft Type and Squawk Code.
If you want to be alerted about Network flights don't forget to check the 'Activate Alerts for Network Flights' box.
You can choose to be alerted by a sound, pop-up box, email or a combination of the three.
Works great here...but one of the things I don't like about Alerts unless I have missed something is there is not a permanent log kept. Although on a current session you can scroll through a limited list showing the type of Alert or move backwards/forwards through the pop-up requestor generated any details that may have been notified along with the Alert are not recorded and as soon as you close RB they are gone forever.
IMHO it would be nice if these details were recorded somewhere for later analysis.
I have posted previously on the type of things I have in my Alert list here as an example;
http://www.airnavsystems.com/forum/index.php?topic=1192.msg8955#msg8955Hope that helps.
Kind regards,
-=Glyn=-