Correct me if I'm wrong, but there is no need for a 2GB SD card as I read in one of the PDFs. I'm aware that the FULL directory will take up almost 2GB, but if you wanted to only update certain files(such as DATA.zip), you only need as much room for those things in order to transfer them on to the unit.
I went and bought a 4gb card, but I realize there is no use for it as one of the PDFs said. If you needed to fully replace the drive, I agree you would. But for small updates here and there, I don't believe it is necessary.