Installing window on the next unallocated space after ubuntu ext3 and swap

Hi all
My problem is opposite of what is normally asked here. I want to install window xp back onto my harddisk. My harddisk size is 80GB of which the first partition is /dev/sda1 ( filesystem is ext3 ) and the next partition is /dev/sda2 ( filename is Linux-swap ) and a balance of 20GB ( unallocated ).

I have experiented this before whereby i reinstalled xp and the grub is missing upon rebooting. I have also google around and understand that i need to modify my existing grub to reenabled it. I have also download super grub disk but i needed more assurance. Does anybody ever try this before and also, can i modify my /boot/grub/menu.lst from ubuntu LiveCD instead of using super grub disk and if somebody can list out the changes to be made to /boot/grub/menu.lst ...that will be fanstatic...

Thanking you people in advance.