Just ran into this situation with a client. HP's driver download page states that the Mac OS 10.5 install disk loads the latest printer driver for the Z printers. But Leopard actually installs an earlier driver (v 4.2.x). The current driver (v 5.1) must instead be downloaded from HP's site. Look for it under the OS 10.2-10.4 pulldown.
BUT, HP Tech support warned that if you're running Leopard, it's very very important to choose the driver only download from the HP site. Keep the HP Print Utility that came with the Leopard install or bad things will happen, like not being able to calibrate any papers.
Hopefully they will correct their web site info and put the 10.5-ready driver where it belongs. Because as I found out today, the older driver does not play nicely with the latest firmware (v 6.0.0.8).
