The free space is from cylinder 5484 to 7396. Since you have already had 4 primary partitions in your system, you may have to,
1. extend partition /dev/sda1 (C:) to include the free space, then install captive/ntfs-3g on your FC5. This makes partition /dev/sda1 (C:) shared by both XP and FC5. You could create a share drive on C:, XP & FC and read/write in it.
2. like redman suggested, delete a primary partition although I don't know which one you could delete. I have no clue what /dev/sda3 is for.