Jakes,
Yes, a Traffic Collision Avoidance System. A very quick look pulled up this gauge on fs.com, but I'm sure we have a few here too.
ilhtcas4.zip
@flightsim.com
Other than that, a standalone gauge is great too! As far as that goes, I'm guessing that you are thinking of employing that certain green radar one that everyone seems to use, but if I may mention a very nice variant of that....it is a similar system but is in color. Green for non conflict aircraft, white for nearby aircraft on the ground, yellow for possible conflict, and red for imminent conflict/collision threat.
It is found in the Chinook by Mark Adams and Tom Woods, on this page (fourth from top):
http://www.simviation.com/fs2004helicopters13.htmIt is a really excellent interpretation of a TCAS system.