I don't have a TI-89, but I am using the TI-84. So I would guess that you would enable the Hermes payload the same way as the 84. Just go under "Options" in the JB program on your TI-89. Then under Stage 1 payload you will want to choose Hermes4b (or whatever you are wanting to run/try). After setting the payload, just do the JB as you would normally (power on, hit eject, etc.). Hope that helps, but again, I don't have the 89 so I could be wrong.