If WMP can still play the files then they must be saved on your HDD somewhere.

In LW, go to My Library - are the songs showing? If they are, right click on a file > locate on disk... that will open your saved folder (where your music's saved) outside of LW.

Or, open WMP & click on the Library tab. Now right click on a file > properties. Now click on the File tab & check Location... that will show you where the file's saved.

Once you've located the files, check this thread for info about adding files to iTunes: How to transfer music to my iPod (& iTunes)