If I am using garage band could I use a quarter inch to usb adapter? I'm not sure if garage band would be able to use this for recording or if it can only use the computer's built in mic
you can plug in any usb/firewire interface to garageband. after you plugged it in you would need to make sure you had the right drivers, then in garageband under preferences you will set the "audio in" to the interface and "audio out" to the built in mode so it can come out through the computer speakers/headphones.
Yes, but only if you're using a line in port, not a mic.