Problems with GNU/Hurd partition

[address@hidden]

Hi 

this is my first report and I'll try to be clear.
I have a PC were i must use SCO UNIX 5.0.5 and linux Red Hat 7.2 with 
Grub installed.
My problem is about the bootload because looks like Grub is not able to 
recognize the SCO UNIX file system.
My partition table is:

linux (hd0,0)   (/dev/hd1)
GNU/HURD (hd0,3) (that means that GNU/HURD is installed in /dev/hd4)

I tried to run grub in teminal typing the commands provided in your 
document at para GNU/Hurd but at the first command

grub> find /boot/gnumach

the response is 

ERROR15:file not found

....ok no problem is the suggestion in the document, but when I type

grub> root (hd0,3)

the response is

ERROR17:Cannot mount selected partition

My question is, what does it mean?
The problem is me or the file system unrecognized by the system?
Please help me....and...no problem about the problem above....I know 
that the problem is me.

Thank you.

Giuseppe