Jonny,
Jeez, I remeber that game. Somewhat unputdownable as I seem to remeber!!
Regarding X-plane, I ain't tried the previous versions but I gather that version 7 is a bit of a leap in a few respects.
Anyway check this out for scenery:
http://www.chromatix.uklinux.net/scenery/download.html. The UK seems to have the airports, nav aids and also seems topologically accurate.