First of all, your kernel version is not a kernel from Red Hat Linux 9. Please look into getting the last errata packages and the newer security fixes for Red Hat Linux 9 from
http://www.fedoralegacy.org
Secondly, the easy way to patch iptables is to fetch the latest iptables src.rpm package for Red Hat Linux 9, install the "rpm-build" package, extract the iptables src.rpm (rpm -ivvh does this, too) and modify the included *.spec file to add and apply another patch. Then use "rpmbuild -bb *.spec" to build the binary package. With a little bit of web searching, I'm certain you would find howtos/tutorials on RPM building, in particular documentation on how to build as non-root user. It's all straight-forward, at least after doing some reading. Though, since iptables examines the kernel configuration, you may need to patch your kernel first with netfilter patch-o-matic (or whatever contains the pptp-conntrack-nat kernel code).
Note that (re-)building src.rpms as root user below /usr/src/redhat bears security risks of all sorts.