I am trying to copy a bootable DVD iso file to a harddrive in a USB harddrive enclosure. Is there anyway to make it able to be booted up? will work?

No, a file of an image in a directory will not be bootable. Also, you are missing "of=" in the command you gave.
A bootable image will need to written to the device itself, as in
dd if=/home/thomas/Downloads/debian-31r2-i386-binary-1.iso of=/dev/<usbdevice> bs=512

It may be better to use something like this:
dd if=/home/thomas/Downloads/debian-31r2-i386-binary-1.iso of=/dev/sdb1 bs=512 .
This will write an image to the partition rather than the entire device. You might need to experiment on whether or not that will work. If you write to the device for the entire drive, you are limiting the size of the drive to the size of the DVD. You may need to mark the partition you do this for as the active partition. It may, or may not need to be first partition.


Your systems BIOS will need to support booting from usb as well.

Question: What is the filesystem used in the USB drive? The fat32 filesystem has a 2GB filesize limit. The image wouldn't be fat32 because you are writing a filesystem to the device.

That probably won't work. Not 100% sure on this because DVD uses UDF as opposed to iso9660 with CDs but a CD filesystem is missing a partition table and some other essential things your BIOS will struggle without. It treats a CD/DVD drive differently to a USB disk and while I may be wrong, my vote is it won't work.

@jschiwal sorry about that....I did use a "of=" in my command. I do realize that i need to be able to boot off of a usb device and i have done that many times before....I have tried copying it inside a partition too. That doesn't work.

@cs-cam are you saying I have to be able to make some sort of filesystem on the device? using dd doesn't work, I cant even read the dvd iso file on it.

A data dvd probably uses iso9660. I have a downloaded SuSE dvd image on my laptop. It is mounted using this entry in my /etc/fstab file:
You can use the "uid=" and "gid=" options as well if you want to. The umask, dmask and fmask options do not work. I think that it is a read-only filesystem.
Using the filesystem type of "udf" does not work in this case.

On my system, I have the image file itself selected as the source. The /SuSEdvd mountpoint is handy for exploring what is on the disc. For example, "rpm -qp /SuSEdvd/suse/x86_64/<package file> --info" for examining uninstalled packages.