I use the rounded block plane like that shown in nick's book, in fact i may have made that one, it is "easy" to do with a beltsander. I think it is fun. I used the cheapest version of the Stanley low angle block plane as a starter. should be available at places like Home Depot and your local hardware store.

You could also use a peice of wood rounded with your normal plane as a backer for a peice of course sandpaper. while sanding may take longer, it will do as good or even better job than the block plane if you are unsure of yourself in the tool mutil...I mean...altering department.