If you're using a mac all you need to do is connect your iPod & iPod will automatically update with iTunes playlists.

However for windows it's different. If you're using LW 4.2, you'll be aware that there will be a playlist in iTunes called Limewire. This is purely a reference to the songs in your LW dwnld folder. You'd need to manually add these songs to iTunes.

You can manually do this by highlighting the files or folder in the library in LimeWire and dragging them into iTunes. They'll be copied into iTunes itself.

For LW 4.2: If these mp3s are in your LW dwnld folder then it'll be the folder called Saved Files in the LW Library.