[CentOS] yum $releasever thinks it's 1 instead of 3

I just upgraded one of my Tao boxes to Centos 3. The usual procedure is 
to do a yum update twice, and all is fine.

This time, I had to rebuilddb before I could run the second yum update, 
and once I started this, yum fails. It says that $releasever is "1.0".

Now I realize I could manually edit my yum.conf and make it go to 3, but 
this may not fix the problem down the road. Can someone tell me where 
this variable is defined, and any suggestions on how to fix this 
problem, please? Might a reinstall of yum packages fix this, as a last 
resort?

Thanks very much.

Steve Campbell