Wow, I had a corrupted filesystem two days ago. Luckily I was able to boot to the flash filesystem, chroot to SD filesystem, enable syslog, figured out why it wouldn't boot and was able to reinstall a couple packages to fix it.

Doesn't help you now but you might want to clone to SD and avoid this situation in the future.

Are you trying to install rootfs on the SD card in a computer and then boot from it on the n800?

You should be able to get rootfs from the firmware image