newbie question : boot problems

[friedt@lpmo.univ-fcomte.fr]

I apologize if this question has already been asked. I've just finished 
reading the archive of the mailing list and couldn't find the answer.
I want to install GNU/Hurd on my laptop (Toshiba Satellite 1625). The
filesystem is as follows :
   Device Boot    Start       End    Blocks   Id  System
/dev/hda1   *         1        19    152586    6  FAT16
/dev/hda2            20       146   1020127+  a5  BSD/386
/dev/hda3           147       273   1020127+  a5  BSD/386
/dev/hda4           274       526   2032222+   5  Extended
/dev/hda5           274       277     32098+  82  Linux swap
/dev/hda6           278       313    289138+  83  Linux
/dev/hda7           314       526   1710891   83  Linux

(hda1 is FAT, hda2&3 are FreeBSD, hda5&7 are Linux/Debian 2.1 and hda6 should
be Hurd).
I downloaded gnu-0.2.tar.gz, un-tared it in /dev/hda6 (with the p option),
and dd-ed grub-boot.image to a floppy disk.
Unfortunately at boot time, root=(hd0,5) recognizes /dev/hda6 as an
ext2 filesystem fine, but kernel=/boot/gnumach tells me File not found.
Does the problem come from the fact that hda6 is on an extended partition ?
Putting gnumach on hda1 (DOS partition) allowed the loading of the kernel
and of the module (serverboot, which was also copied to the DOS partition),
but the boot sequence later fails (at loading servers.boot, which is not found
on /dev/hd0s6 either).

Any help would be appreciated : I unfortunately cannot erase the 1st DOS
partition (from which I load linux using loadlin), and would like being able 
to boot Hurd installed on my hda6.
Thank you, Jean-Michel Friedt
           friedt@lpmo.edu