I stand corrected.
What I mean is that it is just grub.. apparently they added an editor for it. If you want to make that image yourself, all you need to do is use dd, though admittedly you'd have to do some fancy stuff to indicate the location of grub.conf/menu.lst should you want that in your Windows partition.
Frankly I don't see the need for all those shenanigans.
Why don't you use a DVD image?