i'll agree with most here, sdd is quite a boring subject because of the theory. The amount of crap you learn in the subject, and the rellivance to the actual exam, well let's just say, if you know it, you know it, if you don't, good luck learning it.
If you have past knowledge in coding, whether that be web design, actual programming, or even something like mIRC scripting, you will do quite well in this subject (the project side), but if you don't, i suggest you sit down for a week or so, look at some of the basic codes online (say visual basic as that will be something that is commonly picked as the program you study), and see if you can work out the general structure. If you can, do software design, if you can't, i might opt for another subject.
I'm sure most who have done software will agree, the exam itself could be studied the night before, or a whole week, and you could end up with the same mark. The big guns, like algorithms, diagrams and coding debugging are things that can be learnt, but need to be constantly revised. If you already know them, as in had past experience, and know that you can code, then you will do quite well in the huge mark questions.
Take your pick...