Been testing these builds out for a while now privately, and they work very well. I have just been told by the guys at PacketVideo, they will be publishing kirkwood builds for all future releases too.
The current RC build of TwonkyMedia 5.1 for kirkwood/sheevaplug platform is here.http://twonkyforum.com/unsupported/5.1-RC6/
Ther only thing you need to watch, is the media database it creates, gets created in /var/TwonkyMedia so it needs relocating to somewhere other than flash,. if you are booting from onboard flash..
A Wiki page I created a while back for TwonkyMedia on SheevaPlug:http://www.openplug.org/plugwiki/index.php/Run_TwonkyMedia_on_Sheevaplug#How_to_get_it_running_on_Sheevaplug