Flightgear can be so much fun
specially on projectors. Here are some FGFS screenshots running on
our desktop (A circa 2001 P4 Dell PC with a relatively newer NVIDIA
6600GT running Debian Etch)
Happy Landing!
Btw if you dont mind shelling out ~$50, then there is also the
really nice X-Plane (for
linux). It is specially good for instrument flying, has realistic
worldwide airports and scenery (based on SRTM data) and I highly
recommend it.