GRUB2 and /dev/sdb9p1

[Alex]

Hi,

I need to update my BIOS (new graphic card but you don't care) but the 
tool the manufacturer provides is a Windows (only) executable.
VirtualBox can't help me this time as the BIOS is also "virtual".

I reduced my swap partition to let me 2GB for WinXP.
Then I created a fake VirtualBox HDD linked with the real partition :

"sudo VBoxManage internalcommands createrawvmdk -filename /VM/VDI/root/XP_real.vdi 
-rawdisk /dev/sdb9 -register"
(the root privileges are necessary to write on the real partition)


And finally I installed XP from VirtualBox but now I would like to boot 
XP from GRUB2 and... I don't get by.
Indeed, /dev/sdb9 was seen as a whole disk by W$ and that's why, I have 
now a partition table inside my /dev/sdb9 partition.

sudo fdisk /dev/sdb9
Command (m for help): p

Disk /dev/sdb9: 2097 MB, 2097414144 bytes
64 heads, 63 sectors/track, 1016 cylinders
Units = cylinders of 4032 * 512 = 2064384 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xce69ce69

     Device Boot      Start         End      Blocks   Id  System
/dev/sdb9p1   *           1        1015     2046208+   7  HPFS/NTFS



I tried several combinations with drivemap (hd0) (hd0,9), set 
root=(hd0,9) and chainload (hd0,9)+1 ... but XP refuses to boot.

Any idea how I could boot my XP from GRUB2 ?
Thanks in advance