12 volts to 5 volts is easy - just use a 7805 with a heatsink (since it will be drawing more than the rated 1 amps most likely). For -24V you could go over to bg micro and get a couple voltage doubler/inverter chips. This wouldn't provide much power but I suspect it doesn't need much on the -24v line. Now I'm sure people here with EE degrees are going to find this solution horribly inefficient, but it seems like it would work.