What are you using for your default player ???
If you are using WMP you will need to download the codecs to be able to preview...
If you are using the VLC player you will have to preveiw the file from your incomplete folder outside of Limewire, as VLC will not preview directly from LW...
This thread will give you a list of codecs and players you can download....
http://www.gnutellaforums.com/showth...threadid=40665