I haven't heard the Zune. I read that someone said that this beats the Zune SQ. I know it compares to my now deceased Gigabeat F which was the best thing I've heard, especially with rockbox. I've heard that the Gigabeat F was better sounding than the Zune also. Again, I've not heard the Zune so I only know second hand opinions. The T400 is not as customizable soundwise until/if Rockbox ports to it.
Here is a good review with all the pics you should need. I know you can set any JPEG as album art in WMP but I think that is as customizable as it gets.
http://www.geardiary.com/2007/10/31/...-music-player/