Yes, there is an app like Redo Hairstyle that can show you how you look like in dreads. To use it you will have to have gadgets like iPhone, iPad or iTunes. However it comes with a disadvantage that is, it works by placing your face in an oval cut out hence you will not tell how the hairstyle will look like with your actual shape of the face. For more applications, see http://menshair.about.com/od/haircaretips/tp/iphone_hairstyle_apps.htm.
LAFFY you do realize it would take 16 hours at least to get it done and then see the results??? It's not being lazy to try an app that will give you an idea, it is savvy saving of your time - who has 16 hours to just throw away to find out a question that could be answered in a few minutes???