An update on this thread.
I found this freeware program:
Raw Copy by Roadkil - http://www.roadkil.net/program.php?ProgramID=22
This is a low-level program that doesn't try to be clever, but appears to sucessfully do a byte-by-byte clone of any card or drive that a PC can "see", even in the most difficult of circumstances.
My card wasn't bootable, but is was potentially more awkward.
It was an 8GB SDHC card masquerading as a 32GB card (reporting 32GB but only having a valid 8GB memory - yes, an ebay fraudster card) which had hundreds of precious photos and movies of my two year old son on it taken over a couple of months. When the 8GB threshold was crossed, it threw Vista into a fit, which then did a chkdsk that trashed its directory.
Instead of showing folders with 587 photos and 21 HD movie clips, it was showing a FOUND000 directory with 10,000 .chk files.
I desperately wanted to clone the card before letting trial recovery software do their best/worst, and Raw Copy did just that. It happily copied what it was told was a 32GB card to a (valid) 8GB card, generating a clone that behaved just as awful as the source card, but from which I recovered EVERY original camera file from. So it MUST have done a byte-by-byte RAW copy as it said - in my book, that is a superb piece of software.
Whether it does areas like the MBR I know not, but it's low-level operational approach makes that seem likely to me.
For the record, the utility that then did the miraculous recovery of EVERTHING I had lost was another freeware gem:
PhotoRec (over) by CG Security â€“ http://www.cgsecurity.org/wiki/PhotoRec
Keywords: SDHC SD card clone duplicate recover corrupt directory byte-by-byte copy raw
How do I clone an SD card? How do I recover an SD card?