This may not be related to DOS or Windows, but it is in fact related to computers in general.

I recently dug out my failed micro sd card in hopes that I would be able to fix it. What was wrong with it is back in the days of my computer stupidity (though I was still smarter than your average bear), I tried to install Windows XP on it (hey, the partition manager on the setup disc recognized it as a hard disk drive! that's a start, no?). It is slightly less than one gigabyte (961 MB, I think...) and XP setup would appear to partition and format it, but refuse to install on it because it was less than 1 GB. So I had to power off my machine. I booted it from the hard disk drive, and Windows Vista would say it needed to be formatted before use. Upon attempting formating, Windows Vista reported that it was unable to complete the format. The adapter was unlocked.

I found and successfully used this strategy that involves using diskpart to clean and repartition the disk. Doing this will completely and utterly erase your card, with no chance whatsoever of data recovery. Oh well, nothing I had on there couldn't be replaced. And now I have a(n) (almost) 1 GB Micro SD card that I use with my DSi ( with the sd adapter of course).