I have AGB 2.3.1 and PostNuke (PN) 0.723 working together for anyone that is interested. The admin is not integrated in PN - would be nice, maybe I'll do that eventually. There are other GB's that are PN compliant:
A basic GB without the features of AGB can be found on:
place the AGB files into a folder (e.g. Guestbook) under the PN modules directory
in admin/config.inc.php, change:
bug fix in index.php around line 24 - get rid of the period before the = sign so the image path is correct):
to this:
Goto the PN modules page, regenerate the module list, initialize and activate the Guestbook module (not sure if this is really necessary, but can't hurt )
Add a menu item somewhere in one of the blocks (assuming you named the folder Guestbook:
Title: Guestbook
URL: [Guestbook]
Don't use {Guestbook}, the URL syntax is incorrect for this older module format.