I ask about what version of IE, as I believe that the HTML Help application uses an IE HTML control to actually show the content of the CHM file, and I wondered if this control in the Help application was IE-version specific. I'm just brainstorming on what the possible difference b/w my fairly clean installations on five machines and the rest of the world. But in answer to your question, yes, I can open other CHM files just fine.
When I open this CHM file, the Microsoft HTML Help Executable fires up and the "contents" pane on the left looks fine with the iTunes COM table of contents visible. But the pane on the right, the actual HTML content, I see a error screen (not at all like a "help" file, but rather virtually identical to those you see in IE when you have some error pulling up a web page) that says either "Navigation to the webpage was canceled" (when you first fire up the CHM file) or "The address is not valid" (if you try to navigate to any page within the CHM file).
This is very weird, as I've got five different machines, fairly clean installations, with all of the latest software. I just don't get it.
For screen snapshot, see:
http://www.mindspring.com/~robryan/itunesCOM.jpg