[Centos] HOWTO? Upgrade Centos-2 to Centos-3

I've been Googling on this all day, installing GPG Keys, and trying
different yum configurations.  I noticed a similar question in the list a
couple of months ago about going from RHEL to Centos-3, but the answer
wasn't definitive.

Has anyone done this?  Can this be done?  Can it be done with yum?  If so,
how?

When I 'yum update' I get /usr/bin/yum, yummain.main, yummain.py,
clientStuff.py errors, and a "ValueError: unpack list of wrong size"
error.

Would definitely appreciate any direction.

Thanks,
JAB*