Time Machine is a fantastic feature of Mac OSX 10.5 Leopard, but wouldn't it be great if you could boot your Mac from a Time Machine volume in time of crisis?
If your hard drive fails then you need to buy a new one, install Leopard from the original disk plus hours and hours of updates, then restore your Mac from the Time Machine volume.
Well not any more...
Start with a new or reformatted hard drive, which has enough capacity to be used as a Time Machine volume, connect it to your Mac, insert your Leopard install DVD, open Disk Utility and perform a Restore using the new hard drive as the source. When this is finished, go to System Preferences, click on the Time Machine pane and select the new hard drive as your Time Machine volume by clicking Choose Backup Disk. Time Machine only writes to free space so you won't over-write your leopard install. Then next time you have a major drive failure, you simply boot from the Time Machine drive and carry on working!