Stop printer from printing on back.

I'm use my school's printers and their computers when I need to print something. It's set to print on the back of the paper, as well as the front, to save money. I like that, but when I try to print a paper, I can't figure out how to stop it from printing on the back. I've been to the Options, checked and unchecked "manual duplex on front/back" and each time, it prints on the back. What bugs me is that I've done it once before and can't remember how.
It's Word 2007. I usually use XP, but get stuck with a Mac sometimes.
Is there an option where I can stop it from printing on the back?

Also, the printers do it automatically so it's not a manual duplex printer or whatever.