Issue writing image to disk via dd

[Mark Kane <mark@mkproductions.org>]

Hi everyone,

I'm trying to write a bootable disk image to a hard drive using dd in
Debian like so:

dd if=image.img of=/dev/sda bs=1M

dd completes without error and appears to have written this
successfully, however when trying to boot from sda the operating system
does not boot properly as if the image was not correctly written. I
have booted the image directly and know that the image itself is good.

Things get odd because in the course of troubleshooting this I did try
the same exact procedure in another distro just to see what would happen
there. 

Using the same image file and the same dd command in Arch works
perfectly and the image that was written to sda boots exactly as it's
supposed to.

I have tried this on both squeeze and etch where the result is
basically the same. I need to get it working on an older machine that
is running etch however.

Is there anything Debian-specific that I'm missing which might be
causing this?

Thanks very much in advance for any suggestions,

-Mark