For some weird reason, Leopard ships with HP AiO 4.0, while HP AiO 4.0.1 has been available since October.
Even weirder, some Leopard systems pick up the update when running Apple Software Update, while some don’t. And, that’s even taking into account an HP all-in-one printer added to the systems.
Finally, weirdest, Apple doesn’t offer a direct download, nor does HP. Since Apple Software Update is the only way to get it, this means it’s sometimes not an option to download (like, when your system doesn’t pick it up).
So, to wrap all this up, I’ve uploaded a zipped copy of the installer here to download. If you have an HP all-in-one, download the update from the link below: