Installing DBD::Pg

Forgive any blatant ignorance, but maybe someone can help here.

I've installed PostgreSQL 7.0 using the rpm on a Redhat 6.2 setup
and was hoping to do a quick install of the Perl DBD::Pg module using
perl -MCPAN -eshell. This failed and I got the message "please set
the environment variables POSTGRES_INCLUDE and POSTGRES_LIB!". I'm
not sure what to set these to, or even if this approach will work
given that I intalled via rpm rather than having the source. Any
thoughts?

Thanks,
Sean.