I would really recommend doing Multimedia. I did it last year (2009) and got 50/50 and 3rd in the State. What did I do? All I did was make an interactive powerpoint. Utilising technology to enhance your concept is a smart way to go. It makes your work stand out from the bog standard short story, as you are using a number of mediums to create suspense, tone and meaning. Music for instance can give something an extra edge.
In preparing to do Multimedia, I found that there was little if anything to look at in relation to previous works. The only HSC work that I could find was from the 2007 Showcase. I had to look for other similar interactive forms such as DVD Menus and Websites. This helps with form and function (though to a limited extent), thus if you use technology in a simple, yet well executed way, which enhances your concept (most important) then the power of multimedia will win the day victorious.
In thinking about multimedia, look for ways of doing it. Websites are a little static, whereas games and powerpoint give you the ability to create to the limit of your imagination.
My work was based upon the idea that multimedia plays upon the users sense of perspective and discovery. Rather than a website which displays content, an interactive 'experience' can allow you to manipulate the direction of both the perspective and discovery (Think about Linear and Open navigation paths). As in books, films and video games (which I detest) there is a level of suspended disbelief - this is something important to concider!
Hope this helps, keep asking questions I am happy to answer. I know that there is a succinct lack of material and guidance for Multimedia students. But it was that thought of treading on virgin territory and the challenge which drove me.