At least in the first release of Apple's GarageBand '08, the loops are not all installed by default. When you get the dialogBox asking if you'd like to Downlaod them, or install them from the DVD, choose the DVD option and insert either your iLife disc, or Disc#2 that came with your computer, into your Mac so GarageBand can install them (why would you bother downloading what you already have anyway?).
The logic would appear to be that for anyone not planning to use GarageBand, the extra loops and instruments are wasting gigabytes of Hard Drive storage on your Mac for no reason. It also appears that the download option doesn't work for a lot of people, so just use the DVD
GarageBand from Apple Computer uses audio loops and MIDI loops in Apple Loops format. It can work with Audio Units plug-ins. Apple Macintosh Compatible FireWire and USB interfaces can be used to connect Audio and MIDI instruments to your Mac, and be recorded into GarageBand.
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