1. You need to get memdisk. It's included in the syslinux package.
2. You copy memdisk to your boot folder:
e.g. cp /usr/lib/syslinux/memdisk /boot/memdisk
3. You uncompress (if it's zipped) and copy your floppy image to the boot folder, e.g. to /boot/floppy.ima.
4. You create the grub entry, use your normal values for root and the path:
title Floppy Imageroot (hd0,0)kernel /boot/memdiskinitrd /boot/floppy.imaboot
5. Reboot, select it. It should boot normally, only without the annoying floppy drive noise. Done!