Now I need clarification.
What do you mean when you say you 'typed in /dev/fd0'? Sounds like you tried to execute the device file, which would get a 'permission denied' even as root.
If you've opened up /etc/fstab in a text editor and made those changes, you should be able to issue 'mount /mnt/floppy' and, as long as there's a floppy in there, you should be able to access it - 'ls /mnt/floppy' should show the contents.