I'd suggest thinking about how this application will be used. How will future users work with it? I'm sure you know at least a few things about what this application needs to handle, but my first advice is "think of the user and what he or she needs".
Draw it up on plain paper, thinking of where to section off the code. Remeber not to mix logic with GUI code (common error). This way you will be set to extend your applications reach in the future to servlets and/or applets or whatever platform comes along. Section in layers so that you can respond to large changes faster without rebuilding everything. Layers should not see any other layers than their closest neighbouring layers.
Begin with true core functionallity. All that time consuming fluff (that will make your project 4 weeks late), wont matter much to the wast majority of users. It can be added later once you are sure you can deliver on time.
Btw. Even though this has nothing to do with design I'd just like to say that you won't deliver on time. Make a realistic estimate on time consumption and then double it :-) I assume here that you will not be alone in this project and that people will come and go as the project progresses. You may need to train people midway through the project, people go on holiday / need surgery etc.