Try just launching the files with iTunes, that way you'll see whether they play ok.
Go to LW's library, click on Saved Files. Highlight a file & click Explore... your saved folder will open. Right click on a file > open with > choose iTunes from the list.
If they don't play then chances are they're junk. You might've already seen the links below
Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see)

Fake files showing up in search results

And a thread with lots of info about various ways of adding files to iTunes.
How to transfer music to my iPod (& iTunes)


You could try deleting LW's preferences folder & see whether that fixes the problems you're having with LW. Check the link below for more info. Remember that LW has to be properly closed before deleting the prefs folder.
http://www.gnutellaforums.com/335070-post4.html