If this is for fun, then have at it! Put the potato stems up. To actually grow potatoes, you should use one that is a potato seed only because it doesnt have the growth retardant chemical sprayed on it like the ones from the grocery store do. Then you should cut them up and leave them overnight. If you are not being serious about it, I dont see why you cant just take the whole potato and plant it. It grows a bush type of thing and flowers later (that is what they tell me. I just have bush...no flowers yet). Take pictures. I would love to see if this worked or not.

Hi jengc: Yes it is just for fun - now have the bush-type of leaves you were talking about.one on each side of the potatoe - just want to see how this turns out. let you know as it grows more.
Thanks much.