/etc/fstab controls the mount points and options for filesystems mounted under Linux, you don't have to change it if it works.
Windows doesn't care what you've written there. To install windows, make a boot disk (windows will overwrite your Master Boot Record (you won't be able to boot into Linux) ), the boot disk will allow you to boot back into Linux and install a multi-os boot loader. Run the installer, it will simply ignore any partitions it doesn't recognize. Once installed, use the boot disk to reinstall LILO or GRUB. You will need to edit your /etc/lilo.conf or /etc/grub.conf file to add your new installation to the list of boot time options. Procedure will vary depending on your setup, the manpages should help.