TLynnM4591 cover art is only displayed when using the Zune software as the media server. To embed a cover such as a DVD box art you can use a command line switch in mp4box as your muxer but if thats way too technical you can use
mp3tag instead and inject a jpg into an MP4 file.
Cover art and AVI's I cannot say but probably unlikely.
Update: I have posted better
instructions here for MP4-WMP11 along with an update that brings support for 64-bit.
Incidentally for those that are interested I managed to put together a registry file that makes WMP see MP4 files within it's library so the Xbox 360 can now play H.264 videos from WMP11, appears to work okay no major problems encountered yet.
Download registry patch for H.264/MP4 support in Windows Media Player 11.
What's required is
ffdshow tryouts &
haali installed or any other directshow H.264 decoder.
This was tested on 3 different 32-bit Vista machines & worked each time but no XP test, I will get to that later but as long as WMP11 is present then it will probably work.
My suggested install steps
1) Install ffdshow tryouts & Haali media splitter
2) Run WMP disable file sharing (can't perform step 4 with it enabled)
3) Enable hidden files & folders
4) Delete the WMP file database, in vista -> C:\Users\Your user name\AppData\Local\Microsoft\Media Player (just delete everything in that folder and WMP will rebuild the database on the next start)
5) Apply the registry patch
6) Start WMP11 if all goes well it will see the MP4 file types in the video library and playback through the Xbox should also work.
(For those interested H.264/MP4's also work from WMP11 with the PS3)
Edit: The above registry patch does not work with 64-bit Windows still looking into why, the 32-bit WMP under Vista 64 see's the MP4 files in it's video library but does not stream them to the Xbox.