i do ipt and software and seriously, heaps of the stuff overlaps for both of the courses which makes it a hell of a lot easier.... the highest mark question you will usually get will be around 6/7 marks (doesn't include algorithms - which is basically writing out code/logical steps to make something work and trust me, you'll get a lot of experience doing it) and those questions will usually be a page at the most - so its not like you're writing essays or anything.
i am a girl, and although we only have 6 people in our class (all girls), it doesn't necessarily mean you'll be the token female - everyone in our class scored really high. its all about doing past papers/questions and i'm sure you'll find software not too hard.
don't be discouraged by what everyones saying about it being a boring subject - i actually find it to be my favourite subject... like musk said, it all depends on the teacher basically.... if you do have a passion in it, then you're more likely to get a better mark - you'll be more driven to get better marks and hopefully a band 6. just because you don't think you're very good at them doesn't mean you won't go well - the whole point of doing a course is to learn - if you knew everything already, then whats the point?
i will agree with musk that the software developer's view of hardware (which is what i do) is probably a hell of a lot better than the evolution of programming languages, probably because its more logic based (binary arithmetic) and more black and white rather than grey, like evolution is.
in regards to not doing computing studies - 4/6 of our class did it and you probably get more of an advantage in ipt rather than software, and even then its only a small bit.
a good part about software (and to an extent ipt) is that you have to complete a major project. this means that you can put your theory that you have learnt into practice, which helps drum the theory into your head - the heap of documentation that you have to do also helps because most of the questions will be on a case study of some sort and if you've got the experience of doing it with your major, its heaps easier.
hopefully that helps