Short answer is that you should install Wxp first as it wants to install itself onto the primary partition after the MBR, does not want to recognize other operating systems and will overwrite the Fedora MBR with its own boot loader which will deny you access to your Fedora installation.... however now that you are at this point, I believe that you can install Wxp,
assuming that you have a partition setup for it, then you can use most any Linux LiveCD to access/mount all the partitions and install LILO/GRUB to the MBR and add the Wxp partition to the list of bootables.
If you do not have a partition set aside for Windows you will have to resize existing Linux partitions and create a FAT partition using gparted or similar and possibly do some juggling/renaming of these partitions. Am not familiar with FC. It may have a repartioning tool built in.
Check -->
hereGood Luck