lol, firstly, it is noob ("nob" is something quite different
I think fedora core is able to repartition your wimbloez partition so it should remain useable.
If Grub screws up and your Win XP installation is still there, you cana use the Windows discs to go into "Recovery Console" and use the
command to fix the master boot record
although, everything SHOULD run smoothly (beleve me, fedora/redhat have been in the linux business for a long time so there should be few/no problems!
BUT: remember to make a backup of your windows stuff first!