Since the charge port is located way up high and goofy (compared to the rest of the Clie line. . .) you are limited to IR or Bluetooth keyboards, unless you are handy with cables and can figure out how to make a cable extension that would plug into the standard connector from a Sony KB11 or KB100 up to the port on your NZ.
My keyboard of choice is the most recent Palm Universal Wireless keyboard that has the dedicated 4th number row of keys (this distinction is made because Palm's first IR keyboard did not have the number row and to access it was a huge pain if you're entering a lot of number data.) It also has quite a few shortcut keys for Palm OS built-in (most of which do work.) Search the forums for keyboards of choice and you will find others that may suit you, but I'm just not as familiar with them. I know Belkin's wireless is pretty popular. And costs less.