hi
if you download the DSL (DamSmallLinux) distro from the net you can write the image from there.
Download DSL from
http://damnsmalllinux.org/download the ISO of DSL burn to CD
boot the computer with the DSL CD
and im not 100% about this command, maybe some one else can help me
run
dd if=<M0n0wall image> of=/dev/hdc bs=1k
i think the above will do it .. but like i said im not 100% sure you will have to also change the HDC to the USB port
hope this helps and i hope that someone else who know more about linux can step in here ....