You'll need a file recovery program to get them back or you could try using System Restore. LW doesn't send files to the recycle bin, they are deleted form your hdd(In the Beta version there is the option to send files to the recycle bin). I can't offer much advice as I've only used one once, without success(tried to recover some lost e-mails).
Try to use your computer as little as possible until you can run a recovery program so you don't overwrite the files.
See:
DELETING FILES FROM LIMEWIRE LIBRARY-DON"T! - File recovery advice!