I found some nice utilities to make a HD image from a a dir, and another one
for mounting the image on the host, however they are not enough. I need a way
to partition the HD image, and decide which partition will be (ext3 or swap
for example), and most importat: I need to install from the host a boot
loader on the HD image.
The last one is really tricky since last time I tried, lilo did not want to
use a file, but it insisted on a real device. I did not try grub yet.
Well, you can always boot the blank image in conjunction with a boot
floppy/cd and just do a normal install.
On the other hand, if you are really really wanting to do it from the
host OS, I have found this link handy:
http://rescuecd.sourceforge.net/288.html#grub