Zach -- that is the odd thing, most of the Nissan wheels have a "push in and rotate" locking function. Some of the 240SX's have a little screw head that holds in a locking clip. Remove the screw, clip comes out with the center "hub"... replace clip, replace screw, center hub will snap back in place.
Ya, feel like a dummy... but better to see if someone has an idea on how to remove this thing before I break the center out!
Tom