i did it like this..
1.boot with a instalation CD and go on to 'linux rescue' mode
2. mount the root partition to some other path other than root (as it is already mounted)
say mount on to /mnt/root
3. and then i got the /etc/fstab editable.
as i had to do this on te same day...i had to ask my *boss* for this trick
again, i will try your approaches too...no harm in knowing more ways to do.