Just came across a weird one. After doing an in place upgrade of a test installation the Publishing Feature would not activate. Keeps on coming up with an Access Denied message. Ok, so maybe I should have deinstalled WSS 3.0, installed MOSS clean and then reattached the content databases to be on the safe side. But hey, i did say it was a test machine.
The solution is not that obvious though. Looks like the Publishing Feature can't activate because the feature dependency Publishing Resources is not actice. Only solution is to activate the Resources manually via stsadm and then you can activate the publishing feature via the gui.
here's the magic command:
stsadm -o activatefeature -name PublishingResources -url http://YourSharepointSite