Ubuntu on USB without BIOS support / partition unaccessible

Good morning everyone.
New here I'll try to be clear...

Having some troubleshoot with the internal HD of my laptop, I installed Ubuntu 10.10 on a usb drive (in ext4) in /dev/sdb2 - (hd1,msdos2).
The /boot is actually /dev/sda - (hd0,msdos1) formated in ext because the first 32 MB of my internal hard drive are still accessible and it avoids my to need a boot CD. Grub2 is on the mbr of the internal HD. Version 1.98 ubuntu 3.1.

However, when Grub2 boots. I have a message stating that grub2 cannot get C/H/S of partition (hd1,msdos2), which is normal since there is no BIOS support in my (old) laptop but it finally boots (or show me the menu if I press shift) without any problem since it loads the kernel and initrd from internal HD, then recognizes the USB with the kernel/module and uses it as root.

After investigation, i found that in /boot/grub/grub.cfg, I have:

--------------------------------------------------------

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"
if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
  insmod vbe
  insmod vga
}

insmod part_msdos
insmod ext2
set root='(hd1,msdos2)'
search --no-floppy --fs-uuid --set c9083da5-8561-4189-9e7e-d0ef9eed3e55
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi
terminal_output gfxterm
insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set 8812973d-eff0-4248-8007-852e543290c6
set locale_dir=($root)/grub/locale
set lang=fr
insmod gettext
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=10
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###

ETC ETC.

-----------------------------------------------------------

As you can see, after the load_video function, there is:

insmod part_msdos
insmod ext2
set root='(hd1,msdos2)'
search --no-floppy --fs-uuid --set c9083da5-8561-4189-9e7e-d0ef9eed3e55
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi

which of course cannot work since the Usb HD is not accessible yet.

These lines come from the execution of 00_header:

if [ "x$gfxterm" = x1 ]; then
    # Make the font accessible
    prepare_grub_to_access_device `${grub_probe} --target=device "${GRUB_FONT_PATH}"`

    cat << EOF
if loadfont `make_system_path_relative_to_its_root "${GRUB_FONT_PATH}"` ; then
  set gfxmode=${GRUB_GFXMODE}
  load_video
  insmod gfxterm
fi

which uses /usr/lib/grub/grub-mkconfig_lib function's:

is_path_readable_by_grub ()
{
  path=$1

  # abort if path doesn't exist
  if test -e $path ; then : ;else
    return 1
  fi

  # abort if file is in a filesystem we can't read
  if ${grub_probe} -t fs $path > /dev/null 2>&1 ; then : ; else
    return 1
  fi

  return 0
}

It seems this function replies positively whereas the fs is not accessible at boot time.

Strange thing, the first time I installed 10.10 it was working but after a while & reinstalling not anymore...
May be the gfx sceen was disabled for some reason so it did not execute this part of the code. I don't see any option and anyway that would just be a workaround.

I tried using --root-directory=/boot manually for grub-install.

Any idea of how to specify the system some disk is not available at boot time before the kernel ?
And why is just unicode.pf2 copied in /boot/grub ?
Solved in natty ?

Thanks in advance, If we can fix all these little stuff, the system will be perfect !
Bye