Microphone!!!!!!!!

Hey Guys!

So I have a logitech microphone that is suppose to plug into a computer through the microphone input. My macbook pro doesn't have a microphone input, only a headphone input. I have looked at this discussion

https://discussions.apple.com/thread/2036358?start=0&tstart=0

But when I go into the system preference, I don't have a drop down menu?!?!?!?

Please Help!!!

Thanks!