Learning UNIX with a NT background

I have a NT background. I recently started a new position at a software company as a QA Engineer. UNIX seems to be used a lot here. It is my guess that in order to advance, I need to get to know some UNIX in addition to gaining more Windows knowledge. I have the Windows down packed as far as resources to learn from but I’m not sure how to go about getting started with learning UNIX. Can any one suggest any good resources and/or a plan to get started without being too overwhelmed? I have no knowlege of UNIX at this point. Any and all suggestions would be greatly
appreciated.

Thank you