Macbook Pros have 2 different audio ports. One "line in" and the other "stereo/headphone". Both support analog (3.5mm jack) and digital (optical cable, but you'd likely need an adapter).

The 'line in' does not support a microphone. Microphones require power to function, and the line in does not supply power. It can only work with incoming signals that are already being powered (i.e. plugging in an iPod). It's useful mostly for instruments, such as plugging in your guitar amp (not guitar itself) to your laptop for high quality recordings.

The 'stereo/headphone' port has support for in-line mics, such as the apple earbuds. You can tell if your headphones have an in-line mic if the 3.5mm jack has 4 separate metal sheaths, rather than 3. Here is an example.

http://www.iphone-tips-and-advice.com/image-files/iphone-headphone-jack.jpg

There are adaptors you can buy that will combine a mic and headphone jack into a single 4 sheath 3.5mm jack. Here is an example of that.

http://www.amazon.com/Headset-Buddy-Smartphone-Computer-Blackberry/dp/B002SK66OY

Hope this helps anyone else confused over there Macbooks audio ports!