I misspoke. Yum installed kernel-2.6.18-8.1.14 October 13, 2007 according to yum.log. So, yum appears to have worked *once* updating the kernel. Looking in CentOS vault, I saw .15 which gives me a time frame for what it's worth. All I did was add rpmforge. I have removed it with no help. I will post any file related to this mystery when requested.
What does the following command produce on your system?
yum --noplugins --disable '*' --enable updates list 'kernel*'
-Shad