If you have a PPC Mac you could try an emulator, but unless it is a quad PowerMac G5 it wouldn't be playable (and even it would probably be too slow). If you have an Intel based Mac, you can run Windows natively (using Boot Camp) or using a product called Parallels. It would work using the former, but you wouldn't really be running it on a Mac because you would be using Windows on a computer manufactured by Apple. As for the latter, I don't have an Intel Mac so I haven't tried it, but I get the impression the result is somewhat similar to using an emulator on a PPC. You might want to take a look at this thread: http://forums.macrumors.com/showthread.php?t=211626
"Bought and tried Flight Simulator X on a MBP (2.16Ghz, 256vram, 2GB) but it is running so choppy! I cannot get high frames but yet in the demo I was able to play it quite smoothly with the same high settings. If other people are going to try it out on their macs I would love to know how performance is. Thanks"
"My video card is the ATI X1600 with 256mb vram on a refurb MBP 17". I am running Microsoft Flight Simulator X at native resolution however I can only get 7-10 fps with the settings on high (Both scenery and aircraft...I kept the traffic setting on low). I lowered the "Autogen" setting and now I get 12-16 fps. It is playable now but seems to lag over the big cities. When I try to lower some of the settings from Scenery and Aircraft..the fps only goes up by 2-4. So not a majot change. Yet in the demo I would average over 20fps with the same high settings. I even went to try the default airport (St. Maarten) that was used in the demo and it achieved less fps than the demo version. Strange. From what I have been reading in online forums, Flight Simulator X only uses one core of the CPU (now why would Microsoft do that when they know multiple core processors are the future and present). Seeing FSX as both a CPU and GPU intensive game, MS should have designed it to use multiple cores which could have helped with performance."
You could try X-Plane (US$49 - ~1 Gb d/l for demo), it's supposed to be pretty good. You can "build" your own planes if you want to try your hand as an avionics engineer too, or if you can dig up design specs for the F117A or somesuch ;)
It's a universal binary, graphical requirements aren't too high. The demo is highly restricted, only 5 minutes of controlled flight and only scenery for a small patch of California.
The full version download would be a full DVD worth of data or so. They send via USPS airmail (US$12.95) which usually seems to take about 1-2 weeks from experience, or you can pay extra for courier which would be 4-5 days (US$34 postage!)