The Team Fusion patches have certainly helped a lot. The performance a year or so after the game came out was also vastly improved from the base game. If you redownload the game from steam you get the latest offical version.
Then install the Team Fusion patches from here.
http://theairtacticalassaultgroup.com/forum/showthread.php?t=9360Can't guarantee great performance but its certainly worth giving it a go.
A better card would also help, but isn't free like the patches are