Continental A-320-200 Help!

If anyone can help, I'd be in heaven again. The other day, I downloaded the A-320-200 offof flightsim.com, and it looks great. The only problem that I have is with the autopilot. I can't get it to lock onto the gps for nav-tracking. I have noticed that in most of the aircraft with the autopilot, that there is a nav/gps switch. I can't find one anywhere on the 4 different panels. Is there a file that I can download for this? Is there anythingelse that I can do? I really like this plane for many of it's reasons, but the creators have added the seatbelt/no smoking buttons for realizm. Let me know if you can help.......:-zhelp "Never miss an opportunity to fly free" ..Lt. Col. T.J. Palmer, USAF