Create as simple and complete an object-based model for the game board as you can, and make sure that your design meets the requirements given in the project write-up (see the section titled "Project Design")
The initial submission only needs to implement the asterisked error messages in Figure 1.
Use RCS to backup your source files each time you make measurable progress (e.g. finish a tricky method, produce your first 'stub' (outline) for a class/classes, etc.). Avoid updating every time you make a small stylistic change to comments in the code, etc. (however, if you spend 15-20 mins writing comments, you might want to back that up). Also, do not check-in only the final version of your program, as this will cost you points.