Usually the drive must have more than one partition and grub/lilo on it to
fool the OS into treating it like a normal disk.
unetbootin works well to create such things:
http://sourceforge.net/projects/unetbootin/files/UNetbootin/494/unetbootin-linux-494/download
On Tue, Nov 30, 2010 at 03:23, Steve Holmes <steve@holmesgrown.com> wrote:

> I got a new machine which (of course) has Windows pre-installed and
> I'm not ready to dump it entirely just yet so in the meantime, I built
> out a complete Arch Linux 64-bit system on a portable USB external
> drive.  I also used or tried to use grub to set it up to boot.  During
> the original settup session, it appeared to do all this OK but I can't
> get the laptop to recognize or boot from this device.  I did not
> modify the master boot record on my laptop; instead, I figured on
> using the boot menu on the laptop to choose the USB drive; this method
> works beautifully with an ISO image I burned to a small thumbdrive but
> I cannot do the same with my larger USB portable drive on which I
> installed Arch Linux.  Do I have to do anything else to make this
> thing bootable?
> ---------------------------------------------------
> PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us
> To subscribe, unsubscribe, or to change your mail settings:
> http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss
>