I once ask the same question to the guys here. 'Been thinking about getting a MacBook Pro and was contemplating about running FS2004 thru Windows XP via Boot Camp or Parallels Desktop. If you got doubts about FS2004's compatibility with the Mac OS X 10.4, you might wanna check out these alternatives:
[img]http://www.graphsim.com/GeneratedItems/images/X-Plane-8-Box-Front-Flat-small.jpg
X-Plane 8.0
[/img]http://www.x-plane.com/pictures/MartinBalcomb9_sm.jpg
Screenshot (X-Plane 8.0)
[img]http://images.apple.com/downloads/macosx/games/simulation_and_sports/images/flightgear_200604031831.jpg
Screenshot (FlightGear - freeware)[/img]
These simulators are compatible with Mac OS X 10.4 Tiger. Just my 2 cents.