Windows users can't have files automatically add to the iTunes library.

You can turn on iTunes sharing within LW (tools > options > iTunes) & then you should see a shared 'your name's Limewire tunes' within iTunes...this is just a playlist though & the songs aren't actually in the iTunes library (so you can't add them to an iPod). You'll need to add things manually to the library. There's more info here
Transferring music to iPod & iTunes