I have been spending my Spring Break trying to learn how to use my new MacBook computer, which I have found to be a frustrating but ultimately rewarding experience.
The most difficult problem I have encountered has been with Audacity. On my Windows computer it was possible to record non-digital music through an "I" cable that I could string between my source (a mini-disc recorder, a cassette player, a turntable, an external microphone) and my computer. My windows computer, which did not have an internal microphone, automatically recognized the source in Audacity. The MacBook does not automatically recognize the new source, and I was not able to find a way to turn off the internal microphone.
I am really proud to have found a solution to the problem, and by posting it here I hope that I might save someone a bit of frustration.
If you encounter the problem of not being able to change the "default import source" (and you will on a mac), go to the "Audacity Preferences" listing in the Audacity menu, go to the "Audacity I/O" tab, and change the "device" to "Built-in output." You can also change the "Channels" from mono to stereo here.
Another annoying mac-audacity problem is not being able to export files in mp3 format. When using audacity, it simply can't be done on a mac. To get an mp3 you have to save your file as a .wav file, and use a program like Switch (there is a free version) to convert the .wav into an mp3.