Sgt.Pepper, simply do as WW suggested but instead of choosing WMP to open the file, choose iTunes instead. ie: choose an mp3, right-click & choose open with iTunes & tick the option that says always use. You should also do this with m4a files.
jazzbass86, go to LW's menu bar, Tools>Options>Player & disable the media player & press apply button. (click on attachment thumbnail below)
Further reference:
Setting Default video app & also
How to transfer music to my iPod (& iTunes)