You need to install the WiniPac software that came on the disc you should have had with your iPac.
You can drag round the objects you need and re-create your own control panel on-screen, then you assign key-presses to the buttons and hit 'program'. It then saves the configuration to the eeprom on the iPac. Please note though that programmable config is not available on the USB version of the iPac and you have to stick with the default MAME keys, but this shouldn't be too much of a problem as the two functions you need are already programmed to two wires on there. And although you can't program the iPac to set each connection to the button you want, you can still save button configurations as .ipc files on your PC. Then it's just a case of setting up your other emulators to match your keymap.
Go to the Ultimarc website for more support. They give you a colour-code map of each of the wires' default settings, and you can download WiniPac from the website as well.