Havent used an ATI card in awhile, but it cant be that different. Right click on the desktop and select "properties". Then go to your "settings" tab and click on the "advanced" button. Find the tab for your 3D settings, it probably has the ATI logo on it. In my Nvidia controls the menu tree pops out to the right displaying my choices for various screens for settings on my video card. There should be one that says something like "3d settings". Or alternately you can just go through all your choices one by one until you find something that has choices like "Antialiasing" and Anisotropic Filtering" and either Vsync or Vertical Synchronisation or something along those lines. Alot of people will reccomend you have this turned off for performance, and its true that most times your frame rates will go up. But its not truly giving you more performance. Vsync basically "caps" your frame rates at whatever your monitor refresh rate is. That is as fast as you are going to see things refreshed on the screen anyway, no matter how fast your video card can pump out those pixels.
Once you make sure Vsync is turned on, check the refresh rate of your monitor and make sure it is set to the highest number your monitor supports at whatever your desktop resolution is. If you look again at the graphics properties menu, there is a tab that says Monitor. Select that tab and at the top it will tell you what kind of monitor you have, and at about the middle of the screen is a drop down menu that lets you choose the refresh rate. Below that is a check box that says "Hide modes that this monitor cannot display". You want to leave that checked for safety.
Last thing you can check ingame sounds a little silly but.........
I dont often use GVs. One night recently I was playing with PT boats though, and I turned on the Ground View Mode. I never thought anymore about it. The last couple of weeks I have noticed my frame rates in the toilet (for me, I was in the high 20s and low 30s), and the horizon edges were sharp and jagged instead of smooth. I tried every video setting both ingame and out I could think of, and only made things worse. Then I tried putting it in Full View Mode and viola! My frame rates jumped back up, my horizon went back to normal, my terrain was rendering properly again............ Apparently when you change view modes, it STAYS in the last mode you chose, even if you exit the game and return. Or at least it did for me. Flying while in Ground Vis Mode gave me some symptoms like what you described, especially the jerkiness when closing in on other planes. If you have used this recently, might check it. Just hit Shift + F1 and see if it helps.
