I am using a similar configuration as you with a Mac, and just went through a networking issue with my Z3100ps, and it confirmed that with the Bonjour connection active my printer doesn't sleep as it did before recent SW updates.
My solution worked for me. I the Mac Print & Fax Pane, I first trashed all Bonjour printers, and then created LPD connected HP Z printers. Then Open the HP Printer Utility and then select your printer and then go to Additional Settings in the list on the left. Open that and click on Open Embedded Web Server, and then select the setup tab at the top and on the right is a button "Networking." then Click on that and Under the Networking Tab, and down the Configuration list select Other Settings. You will see all the choices for types of connections. Switch off Bonjour, and your printer wil be catching some ZZZZsss.
(or more quickly, optionally you can click on Network Setting in the HP Printer Utility, then Configure Network Settings, then in Configuration list select Other Settings. You will see all the choices for types of connections. Switch off Bonjour.)
Please disregard this if you have already turned off Bonjour to solve this "issue."
So long for now, TOM
Hi, I'm printing via CS4 photoshop and G5 PPc Mac to a Z3100 via ethernet connection (bonjour) and all is good apart from the Z3100 not sleeping after the HP firmware & Leopard upgrades.