When you delete files from the LW library they doesn't go to the recycle bin, they're gone from your hdd. You'll need a file recovery program to get them back.
See:
DELETING FILES FROM LIMEWIRE LIBRARY-DON"T! - File recovery advice!
This has been corrected in the latest Beta version of LW. Files deleted from it go to the recycle bin. Get it here:
http://www.limewire.com/english/content/pro.shtml. It's listed at the bottom of the d/load page.