Greetings Absolutis & welcome to Mint,
It is always better if you are to dual boot to install the window OS first then Mint (or Linux) then grub would be able to find windows and add it to the boot menu
for you. but you can do it the other way also. before installing window xp go here and download a copy of boot-repair. https://help.ubuntu.com/community/Boot-Repair
after you install windows run it and it should re-install Grub for you.
When you install windows xp it will automatically install it's boot loader to the mbr and erase mint's grub bootloader.
follow the instruction on boot repair and you should be good to go.