Please ignore my last post. I have now got Tonto 1.48 working with Snow Leopard and communicating with my Pronto. The 2 important things are: 1) make sure Tonto is running in 32 bit mode (see above) and 2) make sure you are using the correct keyspan driver for your operating system. The CD supplied with the my keyspan converter contained a driver for OS X 10.2.8 or greater and this did not work with Snow Leopard (10.6.5) - Tonto could not find my Pronto. However, the keyspan website has a driver for OS X 10.6x and after downloading and installing this all works correctly. I guess the moral is always check for latest drivers even if you have just bought something!