Previewing can't hurt the file. Your player might be missing codecs? See here for lots of info & also a link to VLC player. Lots of people swear by it:
http://www.gnutellaforums.com/showth...ght=wmp+codecs

See here for how to use Bitzi web lookup to check out before downloading:
http://www.gnutellaforums.com/showth...threadid=37676