I'm really not sure where the problem lies here. I've got a 256MB PNY card, which at least one person has reported success with, and at least one other person has reported failure with.
I can't get it to do anything but fail.
I've formatted it under Windows 2000, Windows XP and Linux. I've tried doing a partitionless "superfloppy" format (mkfs.msdos -I) - the GP2X refused to see anything on the card. I've tried putting just the kernel image on the card. I've tried putting just the bootloader image on the card. Nothing works.
The only things I haven't tried are a different card reader, or a different brand of card, because I don't have either available to me. After reading some conflicting reports about the same brand & size of card, I'm not confident that brand has anything to do with it; my guess is it's either more dependent on the card reader, or some odd combination of card reader & card.
I'm also having USB problems; both Windows and Linux recognise that something is trying to connect, and Windows gets as far as recognising that it's a mass storage device, but neither gets all the way. Unfortunately, I don't have a powered USB hub; from googling the error messages spat out by the kernel under Linux, I have sneaking suspicions that a powered hub would make all the difference.
I can play music just fine. I can play Quake just fine; sometimes, if I'm really lucky, I can even use Quake's savegames successfully. But something's clearly not right. Quake very often fails to either read or write saves (I'm not sure which), and a quick utility I knocked up that does a "find" on the root filesystem - piping the results out to a file on the card - will sometimes work, but more often than not, never complete (i.e. never get back to the menu, and not write a file list to the card).
On an unrelated note, I also knocked up another little utility, that ran various commands ("whoami", "uname -a" and so on) and piped their output to files; that one managed to work once and once only so far. Sadly, I don't have the info any more (I never backed it up before reformatting the card for the umpteenth time), but I can remember that you're logged in as "root", which has no password, and there *are* other users on the system, but you can't log in as them (if I remember my shadow file syntax correctly).
No, there are no executables on the root FS with names like "flash", "upgrade", etc. - I also couldn't find the kernel image. Which means that no, I won't be writing a flash-whilst-running utility any time soon.