Hi, I am a total newbie to 3d printing. I just received my Plastic Scribbler Asterid 2200 printer and am trying to connect it to my iMac through Pronterface (MacPronterface). The iMac is running OS X (10.7.5 - Lion). I plugged the usb from the printer into the iMac and started Pronterface. At the top left corner of Pronterface is the "Ports" button and a drop down menu. When I click on the drop down menu, it says "None" for Ports. How do I get the com ports to show up so I can select one? As you can probably tell from my question, I am not very tech savvy. Oh, this may help, the printer, usb cable and Pronterface all work perfectly on my wife's PC which is running Windows Vista. Any help will be greatly appreciated. Thank you.

Jim