LinuxQuestions.org - Trying to add os to grub

Okay, here goes...

I have 2 hard drives set out like this -
hda1 Linux
hda2 Windows XP
hda3 Backups

hdb1 Windows XP
hdb2 backups

I have been using grub to dual boot between linux on hda1 and Windows on hdb1, the Windows on hda2 was not used.

I've now decided I want to use that Windows on hda2 for experimental purposes but I'm having a little trouble booting it from grub.

If I select the option from the grub menu I get an invalid system disk error - press any key. When I press any key it does boot as normal but I'm just wondering if anyone can tell me how to get around the error.
I can also boot into it by editing the boot.ini on the hdb1 windows but I would rather boot straight into it from grub.

Now, the fact that it is getting past grub and getting to the system disk error suggests to me that it isn't a problem with grub but I'm not sure. Just in case, here is my menu.lst -

Code:

default                0

timeout                10

splashimage=(hd0,0)/boot/grub/splash.xpm.gz



title                Windows XP (hdb1)

root                (hd1,0)

savedefault

makeactive

map (hd0) (hd1)

map (hd1) (hd0)

chainloader        +1



title                Ubuntu

root                (hd0,0)

kernel                /boot/vmlinuz-2.6.10-5-386 root=/dev/hda1 ro quiet splash vga=792 

initrd                /boot/initrd.img-2.6.10-5-386

savedefault

boot



title          Windows XP (hda2)

root            (hd0,1)

savedefault

makeactive

chainloader        +1

Can anyone shed any light?