I have a Griffin Garageband Cable for my guitar to plug into my computer. The only problem is, I want to record through the line-in port for my guitar, but I would also like to record through the internal microphone for my vocals. I cannot seem to figure out a way to do this! Does anyone know how? Thank you very much!
Yeah easy, what you need to do is set up an aggregate device.

Open up audio midi settings (just spot light it its not in garageband) and hit the audio tab up the top, then select aggregate devices. Hit the + and then select line in and inbuilt mic, save it, then in garageband select your default audio device as the aggregate device.
Ah well, my bad. I felt sure using the line in would bypass the internal mic, but there ya go. It's going to sound pretty nasty though.
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