You can turn on AA in the Sim and on your video card.
If you turn it on in the Sim (under 'settings' - 'display') you'll let the sim software render the things you see on your screen. If you have an onboard videocard this is the way to go ...
But, if you have one, you should let your video card do all the heavy work (after all that's what it's there for ;)) and take the load off your CPU and RAM ...
I can only help you if you have a Radeon 9800 XT Pro, because that's the card I have ... As I don't know which card you have I can't exactly tell you how to do it but you might want to check with Nick N or ctjoyce in the
Tweaking & Overclocking section.
Especially Nick gave me a lot of valuable advice on how to tweak my card settings so that I now have a pretty steady 24 FPS and a fluent Flight SImulator experience :D :D
But Cameron is no idiot either! He specializes in overclocking --> he runs a 3.0 Ghz @ 4.0 Ghz

)
BTW: Welcome to the V! Hope you like it here with us. If you need anything just PM me ...