The IPac is a keyboard encoder. As Hoopz said, it's simply plug and play. It already has the default Mame keys built into it, so if you're using Mame there's no need to change anything.
The IPac is programmable if you wanted to do that, which is where the WiniPac software comes in. But that's assuming you have not got the IPac "VE" edition. That's the "Value Edition" which is a cheaper IPac without the flash memory onboard. Andy started selling those recently I would guess because most of his customers only buy it for Mame so he offered a cheaper version.
In actual fact I think you can still program the VE version, but when you switch off you lose the settings because there's no flash memory. But it can never lose the default Mame settings which are built in.