The downloaded % can decrease if there's a corruption in the file: Downloads "Jump" backwards

Check the file with Bitzi, if other users have rated the file then you'll get some idea if it's ok or not
How to use Bitzi
Try to download a different version of the file...see whether that's any better.

If this happens with all files that you try to download - maybe there's something in your setup causing problems (eg a firewall)? In that case, make sure that you're only using 1 software firewall & check that it's properly configured to allow LW. Also check any antivirus/antispyware programs that you might be using: http://www.gnutellaforums.com/245412-post2.html