To get your game looking really nice you will need to activate Anti-Alias.  unfortunately this will have a big hit on FPS. 

Do not enable it through the game though, enable it through your 'Display Properties' bit in the contorl panel.  Click on the last tab (Settings) then hit the advanced button down the bottom right.  You then want to select the tab with your g/card on it (FX5200) then choose 'Performance & Quality settings from the menu.  Turn off Application controlled and set it to 4x for a real smooth picture 2x for better FPS but not quite so smooth.  Also turn Anistropic filtering on here too.  Try 4x or 8x.

Once you have AA on I expect you will have to reduce a fair few things in your game.  Also other games will definately not run as well.  It would probably be best to only use AA in FS2004, turn it off for the other games you play.