Don't know but I have a suspicion that the iTunes library is a little sacred. Don't quote me on that!!!
Yes if you choose to auto import the songs into iTunes you will have 2 copies. That's not an issue for most people. Some use those in the LW Downld folder as a backup to copy to a storage medium. Some people just trash them. You have the option to manually add them to iTunes. See these: 1.
http://www.kapsi.de/files/itunes.html & 2.
http://www.apple.com/support/itunes/tutorial/index.html
Whilst you're having these problems I would advise you set your downld folder elsewhere. Set up a LW folder in your user directory: eg: /Users/your_username/limewire/LW downld folder. Personally I save my files to a different partition/HDD.
I'd also suggest you don't use too many other apps at the same time as LW. Keep using my initial suggestions about minimising ram use. And don't resume all your files to get them started. That can play havoc with LW. Also let LW settle before doing anything with it. Tell us how you get on.