or padlock the PC, password the bios and disable booting from floppies. Thats as good a defence as you can mount against this. If it wouldn't leave such a great hole in the case we would remove the floppies round here.
Better take out USB, CD, and network bootability too
I wake up in the morning, wash my face, brush my teeth, and sharpen my tongue.
Preparation is half the battle, its also a butt cream.