You can use the Live CD to rescue your system. The reason you are having trouble though, is that you are trying to modify the /etc/fstab on the live CD partition, not your computer's hard drive. Here's how to fix it.
Boot up with the live cd. When the system is up and running, open a terminal. You need to find your system's hard drive, then mount it. Use fdisk to examine your system's disk devices.
sudo fdisk -l
You'll see a listing similar to this one.
Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x38000000
Device Boot Start End Blocks Id System
/dev/sda1 * 1 2432 19535008+ 83 Linux
/dev/sda2 2433 38913 293033632+ 5 Extended
/dev/sda5 2433 38662 291017443+ 83 Linux
/dev/sda6 38663 38913 2016126 82 Linux swap / Solaris
On my system, the root directory is on /dev/sda1. I happen to know that my system uses the ext4 filesystem, but yours may vary. (In fact, the Id attribute there tells you, but nevermind that for now.)
So, what you want to do next is create a mount point (a directory) for your filesystem in the live CD environment, then mount the drive.
sudo mkdir /mnt/harddrive
sudo mount -t ext4 /dev/sda1 /mnt/harddrive
If you get an error saying something about wrong file type or something, try specifying the ext3 filesystem. If you get nothing, it likely worked.
Once it is mounted, you can open the fstab in gedit.
sudo gedit /mnt/harddrive/etc/fstab
Remove the offending lines, reboot, and enjoy. If you have any other problems, post back here with error messages or anything you think might help to diagnose the problem further.