ultramatrix:/# apt-get install horde3
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:
  horde3: Depends: php-log but it is not going to be installed or
                   php4-pear (< 4:4.3.2+rc3-1) but it is not going to be installed or
                   php4-pear-log but it is not installable
          Depends: php-pear but it is not going to be installed or
                   php4-pear but it is not going to be installed or
                   php5-pear but it is not installable
E: Broken packages
ultramatrix:/# apt-get install php4-pear
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:
  php4-pear: Depends: php-pear but it is not going to be installed
             Depends: php-db but it is not going to be installed
             Depends: php-http but it is not going to be installed
             Depends: php-mail but it is not going to be installed
             Depends: php-net-smtp but it is not going to be installed
             Depends: php-net-socket but it is not going to be installed
             Depends: php-xml-parser but it is not going to be installed
E: Broken packages
ultramatrix:/# apt-get install php-pear
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:
  php-pear: Depends: php5-common (>= 5.2.0-8+etch4) but 5.2.0-8+etch3 is to be installed
E: Broken package