You can have a "top end" computer, but if you bought it from one of the big dogs, like Dell, it is most likely loaded with a bunch of bloat ware. A flight sim game is very demanding due to all the math used for positioning in a 3D world.
Your top end computer might not have trouble with other games, and only hicups on some stuff in AH2, but if you knocked down the number of processes you have running you may be fine.
Just hit control,alt,delete and click the processes tab at the top. Check the lower left corner for the number of processes running. When I trim miine down I get it to 15 or so. I have a 3.4 CPU (single, not Duo) 3 gigs of ram, and a 256 AGP graphics card. My frame rate doesn't go below 60, and I have everything turned up and running 512 textures.
Mine isn't a top end computer, and is over a year old, but I keep it lean and mean!
