Reinstalling Grub after windows wipes it out is not a big deal, There are many sites with instructions on how to do it using any 'rescue' distribution, including the Fedora rescue disk, knoppix, etc.
Just boot with any rescue distribution, start grub from the console and follow the
official instructions here
Your 'Boot settings' are in the file
/boot/grub/grub.conf
Beware that sometimes windows not only wipes out the MBR but the whole partition table.
It is extremelly advisable that you backup your linux partitions or at least all your important data in case windows decides to take over.
If Windows and Linux are in different HDDs you have an smaller risk but if both are in the same HDD, chances are that you will have to either repartition after you have finished installing windows and restore the backed up partitions or reinstall and reconfigure Fedora and restore your important data.
Then again, Maybe you'll be lucky and your partitions will be there after you install windows and you will only need to reinstall grub. I guess it's better to be lucky and not use your backups than be unlucky and not have backups.
