It all started when I had to replace one of the disks that the software RAID 1 on this machine currently uses. From that moment on I have not been able to boot to the Windows XP that is installed on the fourth hard drive, /dev/sdd. I am almost positive that the problem is related not to Windows but to GRUB, as if I unplug all the other hard drives so that the Windows XP disk is now /dev/sda it boots with no problem.

The problem seems to be that GRUB detects a wrong partition type, which I understand suggest that something is really messed up. This is what I get when I try to follow the steps that until now had worked like a charm:

grub> map (hd0) (hd3)
grub> map (hd3) (hd0)
grub> root (hd3,0)
  Filesystem type is ext2fs, partition type 0xfd

0xfd? That doesn't make sense. /dev/sdb and sdc are 0xfd (Linux raid), but not /dev/sdd:

edel:~# fdisk -l
[...]
Disk /dev/sdd: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00048d89

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *           1       30400   244187968+   7  HPFS/NTFS

edel:/boot/grub# cat device.map
(hd0) /dev/sda
(hd1) /dev/sdb
(hd2) /dev/sdc
(hd3) /dev/sdd

I have been trying to work this out for hours, to no avail. Can anyone point me in the right direction?