..MOST of the marks given in programming tasks are more on the help, documentation, planning and everythign else, about 10%(or less) is on teh proramming side, it's better to finish your reports, and documentation in preference to finishing the program itself.
i am only in year 11 right now, however that doesn't change the way marks are given.
My suggestions? don't choose somethign thaqt will take ages to make, but not too simple either, BOS for example suggest a note keeping program somewhere, however incorporate some nifty personalised features into it, like an option to remind u in X amount of minutes/hours/days etc.
And language? well my SDD teacher doens't know any languages at all.. in class discussions he'll glance accross at me for help for an example in many cases... and everyoneelse in tehclass is doing QBasic, VB6(actually the whole VS6 suite), Borland C++, java, pascal, and some other programming languages, in otherwords, we've got it all.. what does everyone choose to do? QBasic! and what a bad language that is to try and work out where the error in the program is. one person scrapped his past weeks of QB work simply because he must've left a if statement open in teh 5 A4 pages of work.. he soon discovered teh use of sub-programs and has now re-made it all from scratch.
My poitns in summary:
Choose something simple, yet ingenious
Put more effort itnothe written side of things
Choose a language your familiar with, and yet is up-to-date enough for everythign to happen easyily for you.
most of all, don't stress about not completing the program.