I just got an iMac G5, which of course, comes with Garage Band. My wife can play piano well, but we have no keyboard or piano. When we drove to the closest Mac store to buy the computer (4 hours round-trip), they had compatible keyboards and she was very interested in hooking up a keyboard to the computer to play music and record music. So, what keyboards are compatible? Can I only use the keyboard brands carried in the Mac store or will any $100 Wal-Mart keyboard work?