I had the same problem 1 year ago, I tried everything (meaning everything).
this kept on for about 2 or 3 months while trying to figure out the problem.
I could also play other games than AH and had no problems there.
So i bought a new video card and boom the problem went away ?
guess my video card didnt like AH lol.
the videocard i changed was a hercules 3dprhophet gforce2 32mb card, and I got a gainward gforce2 ultra card instead.
No change in the other hardware, so my problem musta been the videocard somhow.
airguard