I recently upgraded to Leopard. Everything was very smooth, except I could not print to my HP 1012 LaserJet that worked perfectly under Tiger. I did some research on the issue, and I found many results and I even made my own solution that I wanted to share here. There are many reports that are conflicting about the solution to get old HP printers to work in Leopard. Some have said the Gutenprint drivers work perfectly, while others have said they don't (either "bad printer personalities" or "missing usb class drivers"). The same conflicts have been posted about some free Linux drivers. Well, after tinkering around for a while, I found out why there were conflicts and how to fix them. Apparently, when you install HP printer drivers from the Leopard DVD, it also installs an HP printer kernel extension. The kernel extension is in system/library/extensions/hp_io_printerclass_enabler.kext. If this extension is on the computer, you need a folder called "HP" within your libraries/printers folder that has the appropriate usb driver. They both need to be present or absent for either the Linux and Gutenprint drivers to work. Here's how it affects the Linux drivers and Gutenprint drivers. 1) If you remove all of your HP folder, but keep the kernel extension, neither driver seems to work. 2) If you keep both the HP folder and kernel extension, both the Gutenprint and Linux printer drivers work. 3) If you remove both the kernel extension and the HP folder, both the Gutenprint and Linux printers drivers work. If the kernel extension is installed, it looks for the HP usb driver in the HP folder. This apparently has priority over anything the Linux or Gutenprint drivers install. In other words, OS X will use the HP driver to run the usb connection. If you leave the kernel extension, but delete the HP folder, the kernel extension looks for the HP folder but can't find it, resulting in the missing usb driver error message. If you remove all traces of the HP kernel extension and HP usb driver, the Gutenprint and Linux drivers will work as they were intended. I hope this helps some people. Apparently, the HP printing in Leopard is a large problem.