Well, all you folks who assumed that I didn't know about su were wrong, I did, that was never the problem. There MAY have been some problem, hda versus hdc, I don't completely understand what's going on there, but what I've been doing is "fdisk /dev/mmcda1", and on that, it's still failing witha "Unable to open mmcda" or "mmcda1" or "mmcda2", I ried all of them.
I treid inserting a known good flash in my CF slot, and it comes up as /dev/hda, so I have tried doing "fdisk /dev/hda", and that comes up slightly differently, with a "Unable to read /dev/hda" instead of "Unable to open ...". Dmesg show a horde of error messages for hda, too many to list here, but they fall into the categories of "hda:read_intr(status=0x51)",or "status=0x04", "hda racal_intr" with the same two statuses (51 and 4) and several "ide0 reset" commands.. I think it points to the fact that it's failing to actually READ the disk, somehow. The disk was already partitioned on my Mac, so that's not the problem.
Anyone know if there's any possible hardware or software difference between the internal and external CF slots?