Are you asking how to setup LimeWire so that the music you download goes into iTunes? If so, then here's how I do it.

1) From Limewire:Preferences:Player, uncheck the box next to "Use LimeWire mp3 player"

2) After you download an mp3, double click on it in your "Downloads" box at the bottom of the "Search" pane. Alternatively, you can click on it once, then click on launch.

Assuming that iTunes is your system default mp3 player, this procedure will: launch iTunes, import the mp3, and begin playing it.

There are numerous other ways to do this and everyone has their favorite, but this is how I prefer to do it. While you're in LimeWire:Preferences, look around a bit. There are a lot of useful options.