Sounds like the user space partition for the internal 32GB of memory has been corrupted. However the partition used for ./Opt etc where your programs get installed is still available (1.38GB of free mem) which is part of the same internal 32GB of physical memory.

I'm not a Linux expert but I'm sure there's a few dozen commands you could issue from the Terminal to show the partitions. (Quick google shows "fdisk -l" would show the partitions (think you have to run as root).

There's also an option to reflash and rebuild the eMMC partition of the N900 as well as reinstalling the firmware etc.http://wiki.maemo.org/Updating_the_t...MC_in_the_N900