The fs is probably corrupt anyway so just take the card out without umounting it.
Your Z may complain, reboot it (without card in), then stick the card back in and see whether it is mounted, if it is try umounting it again, run fsck, etc.
I'm afraid that's about my last idea, bar using a card reader in a PC to do the job?
Si
P.S.
I'm thinking about trying to down grade to an older rom image and see if that gets me through this.
:-D if you can do this then you can also go to OZ surely?