I haven’t had to "hook-up" help in a Cocoa appplication yet since the application I inherited at work already had it working.  But recently, when the application invoked help I’ve been getting the message:

"Help isn’t available for <application name>"

I found this article to help me understand how help is hooked up in Cocoa.

I checked the required metatag and the info.plist values and they seemed in order.  What worked for me is to remove the Help Book Folder from the resources folder and re-insert it.  Be sure to select the radio button titled "Create Folder References for any added folders"

The one thing that is different in my Xcode 2.4.1 version project from the article was that the Resources folder exists inside a Frameworks folder.