Hi James,
Hmm..
I've only used SuppressHttpPort with the Kernel parameter ForceHostP set to 1. Maybe that is the why it's not working?
Kernel is located at bottom of /admin/site-map also. Restart AOLserver afterward..
Aha!
This is a recent addition added to cvs HEAD version circa January 15, 2010. The 5.5.1 version of OpenACS you have has only a partially implemented version.
I believe the easiest thing to do would be upgrading to a version released after that. I'm not sure where the release info is, I can't find consistent release info for the last few versions. Hopefully someone else can chime in with it. I'm running HEAD versions only right now..
cheers,
Torben