I have the Z3100ps GP and run on a mac under Tiger--not Leopard.
For a general discussion on the difference between the Raster (PCL3) and PS drivers, see the topic:
HP Z3100ps GP, PCL3 (raster) vs. PS (postscript) driverhttp://luminous-landscape.com/forum/index....c=19781&hl=pcl3
Also, I mistakenly upgraded to Leopard only to find that neither the drivers nor the APS had been upgraded for Leopard. I fell back to Tiger and am waiting for all to be upgraded before moving to Leopard. I am going to wait till all work on Leopard before moving over. I have heard conflicting stories about the ps and raster drivers working on Leopard. I think some on this Forum are using the ps and raster drivers on Leopard; I talked to a techie at HP who said that the drivers did NOT work on Leopard. Last time I looked at the web site it said the drivers worked on Mac OS systems up to 10.4--which is Tiger, not Leopard.
I just tried to look at the HP site and found most of them down. I found one site not down; it was on HP support for Macs. It said that most print-only drivers (whatever that means) were included in Leopard and then pointed to the list of covered printers. The list pointed to was for all print drivers for Tiger--not Leopard. The Z3100 was on that list. HP might mean that Leopard supports the same drivers as Tiger; HP might mean something else.
I will check the web site again later today and see if I can find out more.