Do you need to be taken by the hand?
If you see a Grub screen pressing the "c" key instead of selecting system to boot will drop you into a Grub prompt where you communicate with Grub directly.
If you type as I suggest in Post #3 by
you tell Grub that you want to boot the 3rd partition of the first disk. In Linux term that is sda3 which should have XP's NTLDR inside. All MS Windows place their boot loaders in the first partition they recognise and themselves can reside elsewhere.
By the command
you tell to boot up the boot loader inside the specified partition.
is the green light for Grub to hand over its control to the boot loader inside sda3 and you should see Xp boots up.
sda3 is likely to be the location of the Xp boot loader because all MS Windows must be booted from a "active" primary partition. The "*" means sda3 is active and in LInux only sda1 to sda4 can the primary or extended partition.
If you prove your Xp bootable then you amend the /bootgrub/grub.cfg to the manual commands you have used.