fstab & mount

Situation:
One logical partition (/dev/hda5) formated in FAT32.
mount -t vfat /dev/hda5 /mnt/fat

Linux can now read all the files in that partition, but only the root has write access.

Neither
chmod 777 /mnt * -R
nor
chmod a+w /mnt * -R
works...
No errors. All the files just REFUSE to be chmod-ed...

But, if I edit /etc/fstab, and added:
/dev/hda5 /mnt/fat vfat users,owner,rw,umask=000 0 0
then
mount -a

Now I can chmod at will. And finally I can edit the documents in the FAT32 partition, while not logged in as root. WHY??
But it all works now, so that's the important thing...