"df -h"

gives output along the lines of:
How can this be possible? It doesn't add up, I should have 2gb free.

Root can write to the partition but users can't.

It's an ext3 partition but I have been mounting it as ext2 under Windows. I had to run
^ I'm wondering if that's caused it.

Perhaps drive geometries have caused the problem? I'll try removing lilo boot appends and see if that helps.

Do I need to regenerate something on the ext3 filesystem? If so how can I do so safely becauase I haven't got 26gb of spare space with which to backup on to.

Try e2fsck /dev/hdb6 followed by resize2fs /dev/hdb6. Mounting as ext2 shouldn't cause a problem however I don't know what the quality of the Windows ext2 driver is.

it is normal as much i know on any unix-linux system.
and this is because allways there is reserved about 5% to root user.this is for emergency cases.
think about system ,what must rise and cant create even cache on disk?and normal users should'nt never-ever be able to fill up this space.

lol

You can override this some way (the limitation for users) but I don't remember how.Was that helpful or what?
Easy fix:Use a different file system AFAIK other file systems than ext2 don't have that limitation.

use tune2fs to change the limit, or change the user/group who may circumvent these limits.

for your root file system this is not recommended. For a data-dump, or storage partition is this off course very annoying.

tune2fs -g <groupname> can be used to change the group.
tune2fs -r 0 sets the reserved block count to 0.
mpe2fs -h shows these settings.