You can only change the icon if you change the media player and make another player the default player for that file type...
i.e.. Use WMP for your music files and then use VLC for your movie files...
To select another player and set it as your default player follow these instructions...
Go to your shared/saved folder (outside of Limewire) you will find this folder by clicking on one of your files in your LW library and clicking explore...
Right click on one of your movie files
Select open with
Select choose program
select VLC
and tick the box that says always use this program to open this file type...
Here's some info on the VLC player...
VLC media player - Overview