iblis% sudo apt-get upgrade                    
Reading package lists... Done
Building dependency tree... Done
The following packages have been kept back:
  locales mldonkey-gui
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.
iblis% sudo apt-get install locales
Reading package lists... Done
Building dependency tree... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
  locales: Depends: glibc-2.5.0-0exp2 but it is not installable
E: Broken packages
iblis% sudo apt-get install glibc-2.5.0-0exp2
Reading package lists... Done
Building dependency tree... Done
Package glibc-2.5.0-0exp2 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
E: Package glibc-2.5.0-0exp2 has no installation candidate