Figured I'd try upgrading again; this time from CentOS 4.5 to 5. When 4.5 came out I quickly tried just pushing the new centos-release and centos-release-notes packages onto the server and do a 'yum upgrade', but it failed trying to meet dependencies (kernel and kudzu, I believe).
So now it's coming time to do some maintenance to Argo and I'd like to upgrade to CentOS 5 finally. I did some research, and it doesn't sound any easier than before.
First, some packages in CentOS 4.5 are newer than what's available in 5.0. This means even anaconda will have problems (I've experienced this before upgrading from an updated FC6 to F7). That thread basically says it's probably easier to wait for 5.1 to come out, then update before 4.6 comes out.
Then there's the problem of yum not working after and upgrade.
And of course there's the guy who had various breakage doing the update manually.
So I'll probably try to do the upgrade manually on my firewall first just to see how it goes. I guess the worst-case scenario is that I have to install CentOS 5 onto some new drives for Argo, then copy the data over from the existing drives. Not the most ideal upgrade path, but it's an upgrade path.