Ok I will try and actually contribute something meaningful here
I go to USC also. About 90% of people who bring their laptops to the classes I'm in have MacBooks, usually MacBook Pros. However, I don't think there's any discrimination against people who don't have Macs. Perhaps disbelief at how you can go through life without the wonder/beauty/etc that is Mac OS, but I don't think there's much judging. In fact, I'd almost say it's the opposite—some of my friends who are comp sci majors look down on me a little for having a Mac instad of a Windows computer!
Long story short, you should be fine with a Windows. I don't think anyone will judge you for having a PC, and if they are, you don't really want to be friends with them, do you?
p.s. Sciencewoman's gif it too wonderfully apropos! They are all "judging" Alexander Ludwig, a fellow USC Greek!