OK, a few questions...
Are you capturing from the fx-1 directly? what FCP are you using? You are positive it was shot in DV? Are you looking on a broadcast monitor?
If you are using the fx-1, make sure the camera is set up properly. On the menu for playback set format to Auto. The blue light on the side will light up if its DV or HDV.
FCP should recognize the camera through firewire, if it doesn't, reboot and repair permissions, etc, and try to get it to work.
There is no magic codec or driver, if its true DV,i.e. test its playback on another DV camera, it should capture fine using the DV capture settings. If you have FCP 5, you will have the capture setting for HDV.
Finally, always make sure how it looks on a actual TV, HDV has a lot of compression so FCP just might not be playing it back right. Also, the capture window preview is pretty inaccurate. See how it looks coming out on a monitor before making your final verdict