install backupmenu, and you can acces all your mass storage data and repair it from a linux live cd.

see this

http://talk.maemo.org/showthread.php?t=68620&highlight=partitioning&page =2

- just install backupmenu.
- restart your phone with keyboard open.
- when backupmenu appears connect the n900 to the pc with the live cd.
- then press w and you would get usb mass storage access and SD card storage access too.
- then you can use gparted if you have ubuntu for repair, delete, resize and do anything with your phone partitions.
you can use fsck from there too, that is more useful than do it from maemo