I found your post, Teresa. Sorry but I have only seen ads for the Verathane system and not actually used it. A drum sander with 36 grit will make short work of the shellac but it will gum up the sanding belts so if you do go this way, get several extra belts. That is probably the way that I would go and you should be able to rent a drum sander about anywhere. Do be sure to seal up the doors and heat ducts with plastic sheeting and duct tape if you sand with either system.
You might just try stripping a small area in a corner to see how bad it is first. If you do go this way, you can get Citristrip in 5 gallon pails. Go to www.citristrip.com, then Contact Citristrip and tell April that I sent you. One good thing is that you just have to get the shellac mostly off. With pine floors that you are going to stain, you want to put down a spit coat or wash coat of shellac first anyway. A little shellac residue left on the floor is not going to cause a big problem as long as it's level and the color is OK.
As you probably know, alcohol is a solvent for shellac but trying to strip a whole floor with it is unsafe. The evaporated alcohol fume are very flammable and you can's see them burn. Don't use it in big quantities, but you can use a little to get off small scattered tough spots of the shellac. Turn off your furnace, water heater, gas stove or similar appliances with a pilot light. Don't use an electric fan and open all the windows that you can if you are going to be doing this for clean up.