u can do one thing which i did once when i faced the same problem:-
1) boot with ur fedora DVD
2) format the fedora partition just to give it the assurance that u r going to do the fresh installation.
3) after formatting the partition to ext3 proceed to the new installation.
4)once the installation starts take out ur DVD quickly , reboot and quickly insert the XP CD.
voilla u r done...but u will lose the fedora...