Believe it or not, the 9500,while better than most, still isn't THAT great of a card. I have a feeling 1024 textures may be pushing it just a bit too much.
Make sure AA and V-sync are set up in your NVidia control panel to "application controlled" and then in the Video Settings of AH (on the first screen before you logon) make sure the AA slider is all the way to the LEFT (off) and make sure V-Sync is turned ON. You can turn it off for testing purposes, but Aces High likes it to be on to prevent screen tearing and rubber bullets...
If you insist on using 1024 textures, you HAVE to download the Hi-Res Texture pack from here and install it, otherwise you're really only running 512 textures, even if it says 1024. Also make sure self shadows (and other aircrafts' shadows) are turned off. You can also adjust the detailed terrain and distance sliders from the video setting after logging on down a bit... this will actually help quite a bit.
If you've already done all of this, then try setting it to 512 textures and just play if for a bit... see if your framerates improve in a crowd. Your other hardware isn't quite 'state-of-the-art'. This isn't even a multi-core cpu. Add in a relatively low amount of RAM (probably slow ram at that) and a not-so-great video card, and I have a feeling you're just expecting a little too much out of your system to run nearly full-boat settings like this.
