Time Machine backups are not bootable and require the Install DVD to serve as a restore. And you don't always have that disk handy. So just partition your Time Machine backup drive and copy the Install DVD to the first partition! This way, your data and the way to restore it stay together.
The easiest way to do so remains SuperDuper!. Be sure to give the DVD's name to the destination partition.
[robg adds: Disk Utility will also do this, as will CarbonCopyCloner 3.]
Mac OS X Hints
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