what fubar said. heres what i typed before my internet died
Maybe have a look in the itunes folder (my documents -> my music ->itunes) and see if there is two copies of it?
Is all your music consolidated to the itunes folder? As in all the music in itunes comes from the itunes folder. Sounds like you may have 1 copy of it in say a limewire download folder and another which has been copied into the ituens folder and both are being displayed. To see where each track is stored right click on it and then "Get info", and the files address should be at the bottom of the window
What I'd do, is sort out the music in itunes so its all perfect with no duplicates etc. then go File > Library > Consolidate Library.