Plug in your CF reader with CF card inserted
If OS X pops up a message saying that the card could not be read, click Ignore.
Open Disk Utility
Select any Partitions of your CF Card that are mounted, and click the
unmount button. The partitions should now appear greyed out.
Select your CF Card Reader in the left-hand column, and click the Info button
Note the ‘Disk Identifier’: e.g. ‘disk1?
Open Terminal
cd to the directory containing the m0n0wall image
Use this command:
gzcat net45xx-1.xx.img | dd of=/dev/disk[n] bs=16k
NOTE: Before carrying out this procedure it is recommended that you disconnect all disks except for your startup disk, as an error in specifying the drive to be written to could cause data loss.