Couple of possibilities here. Either Limewire no longer recognizes itunes as your default player or the cable software is changing the type or creator code of your files to something itunes doesn't recognize. Do the files play OK if imported directly into itunes? If not, then you will need to change the resource info to "mp3" and "hook" using an app like resedit or techtool lite.
I don't know how Limewire recognizes which mp3 player to launch. I don't see anything in the preferences for this.
Hope some of this helps