The shared 'limewire tunes' that you see in iTunes is just a playlist...those files aren't actually in the iTunes library. You'll need to find your saved folder & then add to the iTunes library...then you can put the files onto your iPod
To to LW's library, click on one of the songs & click Explore. Your saved folder opens. Add to iTunes from that folder. There's heaps more info in the thread below.
Transferring music to iPod & iTunes
As for sharing your music, have a look at this thread for more info.
How to share folders