If you're downloaidng the file from the gnutella network, check the file with Bitzi before download. If other users have rated the file then you'll get an idea of it's content & quality.
How to use Bitzi

If you're downloading a torrent through LW then check the comments on the torrent before download. LW isn't a good torrent client. You're better off to use a real torrent app: http://www.gnutellaforums.com/334667-post2.html