Issue with uninstalling postgres 8.1.9

We have a system that came with pg 8.1.9. When I try to uninstall
those RPMs, it works for all the rpms except for libs:

> rpm -ev postgresql-libs-8.1.9-1.el5
error: Failed dependencies:
libpq.so.4 is needed by (installed) apr-util-1.2.7-6.i386

I am not sure what this is about and how to uninstall it. I cannot
leave the "libs" rpm because with it on the system, the equivalent for
8.2.4 will not install. For instance, while installing the
compatibility stuff prior to 8.2.4 --

> rpm -Uhv compat-postgresql-libs-4-1PGDG.rhel5.i686.rpm
warning: waiting for transaction lock on /var/lib/rpm/__db.000
Preparing... ########################################### [100%]
file /usr/lib/libpq.so.4 from install of
compat-postgresql-libs-4-1PGDG.rhel5 conflicts with
file from package postgresql-libs-8.1.9-1.el5
file /usr/lib/libpq.so.4.1 from install of
compat-postgresql-libs-4-1PGDG.rhel5 conflicts with
file from package postgresql-libs-8.1.9-1.el5

How does one resolve this? How can I uninstall "libpg.so.4"?

I am on CentOS 5, and I'm using the rpms for Red Hat ES 5. Thanks for
any pointers!