"I need to keep XP as I can't re-install that"
Why can't you re-install it?
Do you have the product key sticker on the case? If you do you can borrow a copy of XP OEM version, and re-install using your own product key.
Alternatively, if you could get as far as downloading and running this little program - it'll find the product key of your installed copy.
Shows the value of having a backup!!
Otherwise - you can't do what you want.