This tends to be trial and error I'm afraid.
YES. Preload textures, it will help stuttering.
Don't be too frightened to move the graphic detail sliders to the right. It really doesn't make that much difference to the look and will help Frame rates.
DON'T have Anti Aliasing or Anisotropic filtering enabled. Forget about them. Set to Application Preference or off. They will cripple you.
Press Shift + f1,,f2 or f3 for view distances. I found that f2 or 3 helped Frame Rates CONSIDERABLY on my machine.
I have a similar machine to you (see below) and these days it's mid range going on bottom ! Don't expect too much. If you can stay above 30 FPS in a heavy scene that's good. Remember, AH is VERY demanding and processor intensive. All flight sims are like that.
I have 1gig RAM, but it's too expensive really especially if you are thinking of upgrading any time in the next year. 2100 RAM is obsolete now and you won't want to move it to another machine. I don't think 1gig RAM made all that much difference in AH. If you could pick up 512 second hand somewhere it might be worth it.
Reboot your machine before starting AH, especially if you've been playing other games. Make sure there are no programmes running in the background. You don't need real time virus scanning for example, although i would leave firewall up.
Be careful of more esoteric processes tweaks, you can screw your machine for not much benefit!
Thats about it really. Make sure your drivers are current BUT AVOID THE NEW ATI CONTROL PANEL!
Updating drivers is an exagerrated passtime actually. If it's running fine on fairly new drivers you won't get much benefit from the latest.
Good Luck
2000XP @ 1700 (Ambitious overclock:rolleyes:
9800 Pro
1 Gig PC 2100 DDR
MSI K7T 266
Cat 47 Drivers I think
SB Audigy Player