Looks like your hardware is a bit 'over the hill'. Maybe time to upgrade.
In the very least id upgrade the video card to something like a TNT-2 Ultra and try overclocking your CPU. THat should help, but is a short term fix at best.
Fail that, make sure no other programs are running while AH is running - this includes all the little icons in system tray. Use 16 bit color, turn ground clutter off (cntr-c) and try playing with the distance objects settings (shift-f1 - shift-f3) i think...
And stay away from smokey airfields.