Isn't Garageband a program that has a lot of pre-recorded samples on it? If it is the same program I am thinking of, just save it if you wish to put in some samples, and use something else to record, like ProTools, or ProTracks.
I believe you can still record with it, but it doesn't have the same qualities a program specifically designed for recording. You can download more samples, I know that, but I don't know where, so I couldn't tell ya.
By the way, all the loops and samples are royalty free, so your in the clear legally using that program.