Emu48 is the definitive emulator for HP calculators. This is a port for Mac OS X. It has been tested under OS X 10.2.x and 10.3.x, and may or may not work under earlier or later OS versions. But try it out, and tell me how it goes.
Emu48 for Mac OS X is a port of the excellent Windows version by Christoph Gießelink and Sebastien Carlier. A classic (Mac OS 8/9) port was originally done by Pierre Tardy, whose invaluable help made the Carbon version possible.