Great so we can rule out drivers then ^^
Well here is a post I dug up after thinking about it and maybe be your problem, it sounds like you might be Fake Anti aliasing.
djdanlib wrote:
Fake Antialiasing
You can set a higher resolution for your background than the display mode. Doing this will force your graphics card to downsample the image, which will do a weighted average on nearby pixels thus blurring pixels whose neighbors are not the same color. In layman's terms: You'll get simple antialiasing by setting your background resolution (0003 and 0004) higher than your display resolution (0001 and 0002).
Taken from Here. I would take a look at that post, some of it may be a little advance if you are not real computer sauvey however he details this pretty well. If you don't want to dive into that try setting your background in the FFXI config a little lower then your resolution you are using on your monitor instead of even. You can also try and turn off Bump Mapping if it isn't already.
Good Luck to you,