I just checked, and the iptables stuff is not built in to the kernel. Initially I started out trying to keep it lean, but that probably needs to change. Too many people are comin gup with too many creating things to do with these boards 8-)
A quick attempt at enabling iptables in the kernel config resulted in important stuff being DE-configured, so I'm gonna have to try again when I have a little bit more time. (which unfortunately has been in short supply lately).
Just a reminder to everyone, the source package is in the package repository, so anyone can grab the package and make adjustments themselves. You can also pull it from the git repo in the sourceforge project. Patches for additions are very welcome!