Loop device is read only

[vr <debian-user@iotk.net>]

I can't seem to write to an image I downloaded and mounted as a loop
device?

# ls -l /opt | grep floppy
drwxr-xr-x 2 root root 4096 Jun 18 10:08 floppy

# mount -o loop fdbasecd.iso /opt/floppy/
#

# grep loop /etc/mtab
/dev/loop0 /opt/floppy iso9660 rw 0 0

# mount | grep loop
/dev/loop0 on /opt/floppy type iso9660 (rw)

# touch /opt/floppy/test
touch: cannot touch `/opt/floppy/test': Read-only file system

# ls -l /opt
dr-xr-xr-x 4 root root 2048 Sep  4  2006 floppy


I don't think it's the ISO... I downloaded it here:
http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.0/fdbasecd.iso


What could cause my permission to go from 755 to 555?

How can I put some more data into this ISO?



or alternatively... my need is to get a Supermicro BIOS update into a
bootable DOS diskette image or cdrom image that I will then mount as
virtual media with Supermicro's IPMIView tool.  If there's a better way,
please suggest.  Thanks!