apt-get: is not going to be installed

[Daniel Klein <bringa@gmx.at>]

Hey,

while trying to install mplayer from a non-free source, I've come across 
something I hadn't seen with apt-get so far:

The following packages have unmet dependencies:
  mplayer-686: Depends: libavcodec1 (>= 1:0.4.8-woody0.0) but it is not 
going to be installed
               Depends: libvorbis0 (>= 1.0rc3-1) but it is not installable

'is not going to be installed' seems to be because avcodec1 depends on 
vorbis0. Looking into vorbis0, I find this:

Package libvorbis0 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  libvorbisfile3 libvorbisenc2 libvorbis0a
E: Package libvorbis0 has no installation candidate

So there are now packages replacing it. Is there any way I could tell 
avcodec 'hey, you need vorbis0, right? Use vorbis0a instead!'?

And why don't computers speak my language. *kicks the lazy computational 
linguistics building right next to the dorms he lives in*

Daniel