First of all, if you have ever used that card on some computer, make sure that it is not filled with some hidden, OS-specific trash can folder, and that it did not get reformatted to 4GB. If you never had it mounted anywhere besides on the N800 (that is, never took it out, and have not used it on a PC, with the N800 USB tethered as a SD card drive), the card is toast, and half its memory got damaged and was remapped by the card-internal controller, in which case it would be pointless to split format it - you could merely put two 2GB partitions on it, while it still lasts, which probably won't be long.

Sevo