Major panic after upgrade

[Erik van der Meulen <e.van.der.meulen@avondel.nl>]

Hi. I seem to have messed up big time!
I wanted to install onsite-timesheet on my potato box. Because this was
in 'unstable', I edited my source.list to point to unstable.
The installation upgraded a whole lot more than I wanted: perl,
postgresql, and libc6.
Now I am unable to do abount anything because apt-get breaks. I get
errors like:

  Data::Dumper object version 2.101 does not match
  $Data::Dumper::VERSION 2.09 at /usr/lib/perl/5.6.0/DynaLoader.pm line
  219.
  Compilation failed in require at
  /usr/lib/perl5/Debian/DebConf/ConfigDb.pm line 218.
  BEGIN failed--compilation aborted at
  /usr/lib/perl5/Debian/DebConf/ConfigDb.pm line 218.
  Compilation failed in require at /usr/share/debconf/frontend line 9.
  BEGIN failed--compilation aborted at /usr/share/debconf/frontend line
  9.

I am very much lost in here. Does anyone have a clue if I am lost all
the way or if there is a chance to get things going again?

Thanks a lot!

--
  Erik van der Meulen <e.van.der.meulen@avondel.nl>