I'm still running Adobe CS Premium... I really only use Photoshop anymore so I bought the Adobe Photoshop CS 4 Upgrade. When the upgrade asks for my serial number I give it the one that appears in the Photoshop CS "About Photoshop..." window. The Photoshop CS 4 upgrader says it's not valid. Is it possible to upgrade from CS Premium to Photoshop CS 4 or can I only upgrade to the entire CS 4 suite or not at all?