From what I have heard, it is a decent course. Also, the career prospects aren't too bad either. The pay is rather decent too, I believe graduate salary starts at about $52,000 per annum, and obviously, goes up as you gain more experience and years in the field.
A Diagnostic Radiographer will work with a Radiologist, they will provide the images to the Radiologist to examine. The radiographer will have human interaction, whereas a Radiologist generally doesn't.
If you want to do Raditation Therapy, and are interested in it, go for it. But you have a couple years ahead of you before you actually make a deicion, so I really wouldn't worry about it too much.
Me personally, I don't think I'd like to be a Radiographer, to me, it seems very repetetive and can easily get boring, but that is just my personal opinion. But hey, if you think you'll be interested in it, go for it!