xinetd needs start-stop-daemon, which is provided by netkit-base.
ummm, this is not correct, sorry.
Sorry, I thought I'd found a problem. I should probably have just described my experience better: I did a fresh install of gentoo. Then I emerge'd xinetd. It didn't work because start-stop-daemon was nowhere to be found. Then I emerged' netkit-base since it had start-stop-daemon and I was ok. Since it's my first time doing this stuff it's certainly posssible that I screwed up in some other way...