I have an ATI Radeon 9800, 128 mb and I have had no problems with it at all. There are a million things that can affect system performance. Read some of the tweaking guides and try stuff. Look at Windows tweaks, BIOS tweaks, etc.. One time I even discovered that my joystick was causing a slow down!
With ATI you need to remove the old driver and control panel before you install the new one. There is a utility at the ATI site which will remove ALL ATI files on your system. I usually run that before I install a new driver and matching control panel. They also advise to install the new drivers before you install the new control panel. Just thought I'd mention that as driver installation is an opportunity to mess things up. :)
Falcon 4.0 plus all of the patches, mods, addons, is kewl. Don't expect the scenery and terrain to look quite as nifty as LOMAC. If you like realism in a jet sim you would probably like it. It's a classic. You would have to spend some time reading the manual for the version you are running. Gotta do your homework with that one!
Later, Dude.