Installation of php mhash library on ubuntu dapper plesk web server

I'm currently running a web server with following specs:

*Ubuntu Linux (Dapper) Server Edition
*Plesk 8.1
*Apache, PHP 5

I need the php 5 mhash library (php5-mhash) for SIM integration for a site on this box. When I try to install php5-mash with apt-get, I get the following:
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root@hostbox:/opt# apt-get install php5-mhash
Reading package lists... Done
Building dependency tree... Done
You might want to run `apt-get -f install' to correct these:
The following packages have unmet dependencies:
  php5-mhash: Depends: libmhash2 but it is not going to be installed
              Depends: php5-common (= 5.1.2-1ubuntu3.10) but 5.1.2-1ubuntu3.9 is to be installed
  psa: Depends: psa-locale-base-8.1.1
  psa-bf1942: Depends: psa-security-8.2 but it is not installable
              Depends: psa (>= 8.2.0) but 8.1.1-ubuntu6.06.build81070322.17 is to be installed
  psa-fileserver: Depends: psa-security-8.2 but it is not installable
                  Depends: psa (>= 8.2) but 8.1.1-ubuntu6.06.build81070322.17 is to be installed
  psa-firewall: Depends: psa-security-8.2 but it is not installable
                Depends: psa (>= 8.2.0) but 8.1.1-ubuntu6.06.build81070322.17 is to be installed
  psa-vpn: Depends: psa-security-8.2 but it is not installable
           Depends: psa (>= 8.2.0) but 8.1.1-ubuntu6.06.build81070322.17 is to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
=============================================================================

How should I resolve these dependency issues? I'm hesitant to apt-get -f install for fear of breaking this production web server. I tried enabling all the repositories in sources.list with no luck. Any ideas?

Thank You.