We were given a 128MB memory simm when we bought our 700MH iceBook. It was not recognized either. The fella who swapped out the memory said, as I understand it, the iBook (other Macs too I suppose) read the "name" of that memory module and compares it to an internal list of memory chips. If the chip was not on this list, the computer will refuse to recognize it. So it's not necessarily a matter of electrical compatability.