I have had issues with getting Amarok2 to play under Ubuntu 9.04.
I had issues with it as well.
You need to install:
systemsettings
FFMPEG
gstreamer0.10-ffmpeg
libxine1-ffmpeg
Then run systemsettings
open the multimedia button
click on the backend tab
move xine to the top of the list
click apply
Hopefully things should then be working