For Mac OSX, if your file icons in LW are blank, it generally means you have no default program set to open those files. For music files, set iTunes as the default. For video files, get this player VLC - (click on link) _ (choose nearest mirror site). My guess is you have QuickTime player set as the default video player but you're lacking the correct codecs/plug-ins to play certain types of files. So .. to make VLC your default program for all video types, select an mpeg file & make vlc default. Do the same with mpg, mov, & avi. More about how to do this in OSX here: How to change default program in OSX

BTW most files with the MOV extension on Gnutella network are spammed porn files. Especially if they are less than 100 MB in size.