Yes it is easier to do it through the inner fender well. Here is a video made by an actual Infiniti technician for changing the bulb and the ballast should be nearby. If you're going to lift the car and be under there, it may be a good idea to upgrade your bulbs too.
I suppose its best to do your own research for a replacement and pick the brand you like best, but I would recommend Morimoto for BOTH bulbs and ballasts. I'm told Matsushita makes the OEM ballasts for Infiniti vehicles, but haven't verified that.
http://www.youtube.com/watch?v=ShSW-Vq7T1M