I did COMP123 last yr, wasn't as easy and straightforward as you'd think it would be. Like every subject you have to know your stuff well. I spose if you're already a computer nerd then you'd ace it, but for me I had to study heaps and still only ended up with a credit (2 off a D though).
I pretty much just summarised the textbook for study, and then went over the lecture notes and chucked stuff in from them that I didn't already know (most of the lecture notes were basic stuff). I don't know how much the course has changed since last year though, prob quite a bit :s