Are you using Windows? In LW tools > options > iTunes. Tick the box to enable iTunes sharing > apply > ok.
That shared "LimeWire Tunes" that you see in iTunes is just a playlist (files aren't actually in the iTunes library)...so you won't be able to create playlists or add to your iPod from that list. You'll have to add files to the iTunes library first. Check out the link below for heaps of info
Transferring music to iPod & iTunes