Limewire has an iTunes section in Limewire Preferences. It lets you select how you want to handle your Limewire downloads with regard to iTunes.
If messing around with these setting doesn't get you what you want, click on Limewire preferences to see where Limewire stores the downloads. You could always click on one, or command click to select several songs at once, and drag them into your iTunes library via the finder.
First open my documents & create a new folder. Name it something like "limewire songs to transfer to itunes" or whatever you want. Click on explore in limewire & drag the songs you want into the folder you just created. Go to itunes, click on file, add folder to library, and find the folder you created. (It will be under My Documents as long as that is where you saved it. Click on it & then click on OK and your songs will be in your library. Whoever said nothing is free?
You may want to check on the Limewire website as you probably won't get much help in these forums since Limewire is frequently used to share music illegally.