I would think the HP program would have to be active to detect media and overcome the auto-play settings. You should be able to disable it in startups. Start > Run and type
msconfig. Go to the startup tab and uncheck anything that might be HPPE. If you can’t recognize it you could look it up in the list here:
http://www.pacs-portal.co.uk/startup_content.php
I would guess HPPE was installed before Photoshop and Photoshop linked to HPPE DLLs rather than install duplicate copies. The uninstall applet is supposed to check for that, but they sometimes foul up. You might also uninstall Photoshop and reinstall it after uninstalling HPPE.