Sometimes I'll see a question I'd like to try and answer, but then I notice that the poster's Rep is much higher than my own. Seeing as I'm just a Comp. Sci student, I'm reluctant to answer these questions as I feel it's disrespectful that I should challenge a professional's knowledge/tread on anyone's toes.
How should I handle these situations?
Go for it! Even Jon Skeet has twenty-three questions. If questions were only replied to by people with higher rep than the asker, he'd never get answers!
Rep doesn't mean everything; it's only a proxy measure for competency and knowledge. I've personally got almost as much rep on SO as John C. Randolph. Does that mean I know almost as much as he does? Not a chance! He's been programming in my chosen framework/language for a hell of a lot longer than I have. Another example: Brad Cox invented a language, and he's got 544 rep on SO from one answer. All that means is that he doesn't waste his time on SO!
As Wesley pointed out in a comment, it's more than possible to accrue quite a good amount of rep just by hanging around a lot. You can't take rep as a guaranteed mark of a quality answerer; someone who just keeps posting will pick up votes here and there, and maybe even hit 10k from posting questions alone.*
Furthermore, you can't know what a person's background is based on that stupid little number. You're a CompSci student with 700-some-odd rep, and I'm self-taught with 6k. If I've got a question about the intricacies of algorithm analysis, I sure as hell want someone like you to help me, no matter if you have 1 rep point!
Aside from formal training there's also the fact that, as Bo pointed out, many people have a lot of rep in a narrow focus. Most of my rep is from answers on, essentially, a single technology. When I have a question about another language or tool, I'd hope that anyone who knows the answer will help me, rather than assuming that my rep means that I'm some kind of master geek.
Don't pay too much attention to the number. (It's really just a psychological trick to keep you hooked on SO.) Judge whether you should respond to a question only by the question itself. If you think you know the answer, type it out and post it.
You've got nothing to lose; even if you end up being wrong, you'll probably learn something from others' responses to your post. As you yourself proved after asking this question, many times you will have better information than someone of higher rep. You'll also be helping make SO more interesting and useful, and in no time flat, you'll be intimidating the newbs yourself.
*This is partly by design -- rep is also meant to measure is your level of familiarity and engagement with the site.
Answer the question if you feel you can.
Nothing else should enter into it.
Some people can get a lot of rep from a very narrow field. That doesn't mean they are experts on everything else!
Outside of that speciality you might know the answer. If you do, please tell us so we can learn!
No one is expert in everything. Even my children know things I don't know.
If you know the answer, or a clue to finding the answer, post it.
