The following does not work:
$ gst-launch-0.10 -v playbin uri=http://www.cavestory.org/xm/kingstheme.xm
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
/GstPlayBin:playbin0/GstDecodeBin:decodebin0/GstTypeFindElement:typefind.GstPad:src: caps = audio/x-mod
/GstPlayBin:playbin0/GstStreamSelector:selector_audio_src0: active-pad = NULL
/GstPlayBin:playbin0/GstQueue:preroll_audio_src0: min-threshold-time = 2850000000
** Message: don't know how to handle audio/x-mod
ERROR: from element /GstPlayBin:playbin0/GstDecodeBin:decodebin0: A Module Music Format (MOD) decoder plugin is required to play this stream, but not installed.
Additional debug info:
gstdecodebin.c(988): close_pad_link (): /GstPlayBin:playbin0/GstDecodeBin:decodebin0:
No decoder to handle media type 'audio/x-mod'
ERROR: pipeline doesn't want to preroll.
Setting pipeline to NULL ...
/GstPlayBin:playbin0/GstDecodeBin:decodebin0/GstTypeFindElement:typefind.GstPad:src: caps = NULL
FREEING pipeline ...

But downloading the file and playing it manually does:
$ gst-launch-0.10 -v playbin uri=file:///tmp/kingstheme.xm

Reported in Ubuntu:
https://bugs.launchpad.net/ubuntu/+source/gstreamer0.10/+bug/368846