8.4 -> 9.0 upgrade difficulties

I am attempting to upgrade from 8.4 to 9.0 via parallel install of 9.0
along with 8.4. It isn't going well. Fortunately it's a dev/test machine
I'm using as a test and practice space.

The place I'm stuck is that "postgresql-server conflicts with
postgresql90 (yum output at bottom).

History:

I've mostly been following:
http://people.planetpostgresql.org/devrim/index.php?/archives/48-What-is-new-in-PostgreSQL-9.0-RPMs.html
and
http://people.planetpostgresql.org/devrim/index.php?/archives/50-Upgrading-from-8.4-to-9.0-on-Fedora-Red-Hat-CentOS-using-RPMs.html

The machine was originally built with CentOS 5.3. I installed the PGDG
8.4 RPMs from yum.pgrpms.org. The machine has been in-service for a
couple years during which it has been updated and is now up to CentOS 5.6.

Upon reading that the RPMS are now being built so that multiple versions
can peacefully coexist, I attempted to install
pgdg-centos-9.0-2.noarch.rpm but got an error saying that there was a
conflict with /etc/pki/rpm-gpg/RPM-GPG-KEY-PGDG from 8.4. Reading that
there were still issues that required forcing, I forced it.

Recalling the key-conflict issue from a year or so ago, I erased both
the pgdg-centos-8 and 9 rpms (just the basic ones that update the repo,
not the server/client/contribs), reinstalled the latest
pgdg-centos-8..., ran "yum clean" then "yum upgrade" then confirmed that
8.4 was up to 8.4.8 and working.

I then installed the pgdg-centos-9... repo rpm without trouble. No more
key conflict messages and "yum list" shows both the 8.4 and 9.0
packages. But 9.0 still refuses to install:

Resolving Dependencies
--> Running transaction check
---> Package postgresql90-contrib.i386 0:9.0.4-1PGDG.rhel5 set to be updated
--> Processing Dependency: postgresql90 = 9.0.4 for package:
postgresql90-contrib
--> Processing Dependency: libossp-uuid.so.15 for package:
postgresql90-contrib
---> Package postgresql90-server.i386 0:9.0.4-1PGDG.rhel5 set to be updated
--> Running transaction check
---> Package postgresql90.i386 0:9.0.4-1PGDG.rhel5 set to be updated
--> Processing Dependency: postgresql90-libs = 9.0.4-1PGDG.rhel5 for
package: postgresql90
---> Package uuid.i386 0:1.5.1-4.rhel5 set to be updated
--> Running transaction check
---> Package postgresql90-libs.i386 0:9.0.4-1PGDG.rhel5 set to be updated
--> Processing Conflict: postgresql-server conflicts postgresql < 7.4
--> Finished Dependency Resolution
postgresql-server-8.4.8-1PGDG.rhel5.i386 from installed has depsolving
problems
--> postgresql-server conflicts with postgresql90
Error: postgresql-server conflicts with postgresql90
You could try using --skip-broken to work around the problem
You could try running: package-cleanup --problems
package-cleanup --dupes
rpm -Va --nofiles --nodigest

Thoughts/suggestions?

Cheers,
Steve