I was using PostgreSQL 8.4. I tried removing it through Synaptic Manager and then I tried to install 9.1, but I still version 8.4. I deleted all the files associated with postgresql. Now I am unable to install any version of PostgreSQL. When I try I get this error:

Setting up postgresql-9.1 (9.1.3-1~lucid) ...
.: 12: Can't open /usr/share/postgresql-common/maintscripts-functions
dpkg: error processing postgresql-9.1 (--configure):
 subprocess installed post-installation script returned error exit status 2
dpkg: dependency problems prevent configuration of postgresql:
 postgresql depends on postgresql-9.1; however:
  Package postgresql-9.1 is not configured yet.
dpkg: error processing postgresql (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
                                                                                                          Errors were encountered while processing:
 postgresql-9.1
 postgresql
E: Sub-process /usr/bin/dpkg returned an error code (1)

Please tell me the way to remove postgres completely so I can install a fresh version.