At least in the first releases of these versions of Apple's GarageBand, the loops and software instruments are not all installed by default. You'll need to do a custom install and select GarageBand's ancillary files. The installer should be on one of the discs that came with the computer, likely labeled: Software Restore, or Additional Software, or some such, if not an iLife disc itself. It may also simply be an installer on one of the restore discs called "Additional Software" or something similar.
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...at least for the majority 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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