Here's how I organise my mp3s. Firstly, I don't bother trying to do anything with them in Limewire (other than download them, of course):

I have my Limewire shared folder in Favourites in the Apple menu. To do this, find your Limewire shared folder (command F in the finder and type 'shared'), control click on it and select Add to Favourites. It's now accesible by going to the Apple menu>Favourites.

To move my downloaded mp3s to itunes, I open itunes, make the window smaller, open the shared folder next to it and drag mp3s from the shared folder directly into itunes.

If itunes doesn't accept the file, I drag it over itunes associator (on the desktop) and drag it into itunes again.

To burn an audio CD, I drag mp3s directly from itunes to Toast (Apple's CD Burn software doesn't work on my external SCSI recorder). You should be able to drag mp3s from itunes onto the desktop, into a folder or into another compatible application (such as Quicktime Player).

If you're downloading a lot of mp3s, it's worthwhile moving them to your itunes music library and classifying in folders by artist, album and genre rather than leaving then in the Limewire save/shared folder where they'll be mixed with other text files, software or videos that you've downloaded. You can then add your mp3 folder to be shared by Limewire in Tools>Options>Sharing>Add.