I am assuming that you installed grub as your boot loader? That should replace the Windows boot loader. Are you able to boot into Fedora? If so, see if you can mount your Windows partition there.
Then, check your grub.conf file. It should be located in Fedora at /boot/grub/grub.conf and you should be looking for a windows option (usually commented out). You'll want something like the following:
map (hd0) (hd1)
map (hd1) (hd0)
You may have to chante the map commands to reflect which partition you have XP on.