Well, I'm used to rmxp spriting, but I'm pretty sure they work the same way. In RM2k3 the sprite sheet is 4x3, and is somewhat confusing. Basically, what you need to do is just resize the sheet. RM2k3 divides the sheet into 1/12 of the original size, and in each of those 12 it makes boxes you need to put your chars. basically, just enlarge a blank image to be big enough to fit 12 frames, make sure that the dimensions are right, put in your sprites, and see if it lines up correctly by playing them in your game.