It's hard to say as Vista is so new, but I will have ago...
m3u is a playlist file and contains the location of songs in a playlist...
Now we need to find your shared folder which the mp3 files are saved to....
To find this folder click on one of your mp3's in your limewire library and click on explore...Your shared folder should now appear.... Now try dragging and dropping each file into a new playlist in your itunes....This is how it would normally work, but one of the develpers have suggested a problem with Vista...
This link will explain...
http://www.limewire.org/forum/showpo...66&postcount=2
Let us know how you get on...