Hey Brian,
The sim crashes at various times. Its always after I have been flying one plane then go back to the menu screen. I can sometimes select a new plane or field to fly at and when I click "Fly" it crashes. Sometimes I just hit the button to select a new plane and it crashes. I too am also running a Navidia GeForce 6800 card on a 3.6Gz machine with 2 gigs of ram. Maybe I should try downloading on old update as well?