Formatting the windows partition will not overwrite the master boot. If you reinstall windows, it will overwrite the master boot sector. In that case boot up with a Knoppix CD, mount your Knoppix partition, as rw, from a root terminal do a chroot to the mounted Knoppix partition and then grub-install /dev/hd? where the ? is your boot drive, most probably a, the first hard drive. Exit to get out of the chroot and then exit from the root terminal and it is all back together.