[Yum] Yum-arch -c: why postgreSQL 7.4.2 for RH9 from postgreSQL.org fails?

[Sanjay Arora]

I downloaded the latest 7.4.2 postgreSQL rpms for RH9 from
www.postgresql.org rpm --checksig confirms that signatures/MD5 of all
the packages are ok. On being copied onto my local yum repository and
running yum-arch -c , they all fail the test.

What is happening? Do I have to get some gpg public key of postgresql
people and add it somewhere? If so, how? What exactly is yum-arch doing
with -c...is it only checking for RH sigs?

Sanjay.