To format the internal memory card on an n800 when having trouble.

Method 1 with USB
1. Open the Control Panel and click the Memory Icon.
2. UN-check the "extended memory box" (this is what is using the internal card)
3. Test by plugging in the USB if it doesn't work then do steps 4 otherwise, skip it and go to 5
4. Shut down the n800 and switch the internal and external card (don't worry it won't hurt anything.)
5. Turn the n800 back on when booted plug it into your Windows system (PC's where built by IBM.) and format the external (formally internal) disk. Make sure you do it fat32 not fat16 as fat32 is the one used on SD cards especially if you have a SDHC (4G or larger) card.
6. Turn the n800 off (if you did step 4) and switch the cards back.
7. Open the Control Panel again and this time check the box for extended memory.

Done.

Method 2 without USB.

1. Do step 1 above.
2. Open Xterm and type (where # is your prompt)
# sudo umount /media/mmc2
# sudo mkdosfs /dev/mmcblk0p1
# sudo mount /media/mmc2
3. Do step 7 above.

Now on an n810 you have a different scenario. The internal memory is not an SD card or a disk in the normal sense. It's actually a PROM of sorts (I know it's not called a PROM) where you don't/can't format it, you have to flash an image onto it. So if you want to "format" that part the only thing you can do is flash it.

Unlike magnetic memory (a HDD for example) it doesn't have any sort of memory retention from flash to flash. Nor is it a block device that can be formated. The actual block device is the image you flash on and if you wiped it out and re-flashed it would be the same as just re-flashing.