Further to the previous posts on Apple's deliberate breaking of compatibility with iPod Download, a legal and legitimate plugin that Apple's customers freely chose to install on their computers, which Apple disguised in a disingenously named "update":
It turns out that Apple's system for disabling the plugin uses a blacklist of disallowed iTunes additions in the iTunes binary. If you open the binary in a hexadecimal editor, like HexEdit, you can find the area where Apple has inserted the string "iPod Download" in its blacklist and simply replace the text with something else (in fact, I think you could probably just change one character) and your iTunes's original functionality will be restored.
