[CentOS] problems with "yum --enablerepo=centos upgrade" command

On CentOS 4.5, I'm trying to upgrade MySQL 4 to MySQL 5.

(I enabled the RPMforge with the repository protection)

rpm -qa | grep mysql

gives me:

mysql-4.1.20-2.RHEL4.1.0.1 mysql-server-4.1.20-2.RHEL4.1.0.1

But when I try to update

yum --enablerepo=centosplus upgrade mysql-server

I get

Loading "priorities" plugin Setting up Upgrade Process Setting up repositories Reading repository metadata in from local files 484 packages excluded due to repository priority protections Could not find update match for mysql No Packages marked for Update/Obsoletion

I suspect that something here has to do with this not upgrading properly?

[root@localhost bin]# rpm -qa | grep priorities yum-plugin-priorities-0.0.3-1.c4