As others have said 'teaching computer labs' is a bit ambiguous. The fact that you are talking about a 100 series class, I'm assuming means something more along the lines of 'how do I work in this linux based computer lab', not 'how do I learn everything there is to know about linux'.
Though the majority of the people here are flabbergasted that those in a CS class haven't touched linux already, it is a different time. Keep in mind, those same people haven't touched VMS . . or punchcards. A brief history of linux and why it is useful couldn't hurt. Some key notes like the number of systems that use it for web based systems can bolster the view that it isn't just some basement nerds hobby OS. Brief = Brief, keep it 5-10 mins to keep eyeglaze from setting in. Some of the students are there for the joy of learning, some are there just for the degree so that they can make money. A few stats on how linux = money for them personally would be good, avarice is a motivator.
In your shoes, I think I'd cover the basics you'd need to know in any OS first. "How do I copy a file?", "How do I move a file?", "Can I get that deleted file back?". Moving up to how do I use the editors (both GUI and CLI). Knowing vi is great and all, but it can be a big mouthful the first time you look at it. Keep it simple. Most importantly, teach them how to find the answer to their questions when you aren't there. Linux has been around long enough that there are often a dozen ways to accomplish the same thing and some of the advice out there is outdated or just convoluted. Having some prepared cheat sheets for them would probably be good.
Once you've had time to cover the basics, spend time doing question and answer. You don't necessarily know how much exposure these people have had to Linux. They will have had experience with windows or mac os (and hopefully you have too). Let them ask 'How do I do X in linux that I know how to do in -myOS-'. This is of course dependent in how expert you are with those OS's. If your answers end up being "Its much easier in linux, all you do is X" you are going to win converts. If you can't give an easy answer, don't try while standing in front of them and fudgin your way through it; note it down and get back to them tomorrow. If you've ever watched someone try to figure out an answer in front of you, you can get misdirected by the different places the knowledgable user checks to get to the end goal. Many freshman enter university with a laptop, have them bring it with them. Often they can show you what they want to do quicker than explain it.
Cover the things they care about. If they don't know pidgin, show it to them (and how to remove it since these are shared machines). Here's your facebook page (I know, I'm ill suggesting it too), here's a feature rich office app to try out, and anything else the kids on my lawn care about.
Finally, show them how to interact with linux systems using their OS of choice. Just because you run windows doesn't mean you can't be a linux fiend. If they can get on servers remotely via SSH, show them how so they can keep poking at their own pace.
I wouldn't encourage them to install linux on their personal systems if they aren't familiar with it; they'll end up frustrated when they don't know how to accomplish a task and can't figure it out before the next time they get in to ask you. The minute they reinstall back to Windows/osX, you've likely lost them.
I'm a bit confused why a sophomore is teaching those 1 year behind... The professor is surely paid enough...
