How do I restore my OS X installation from Time Machine backups?
To restore your Mac OS X installation from a Time Machine backup, you will need your Mac OS X 10.5 install DVD. Restart your Mac and hold down the ‘C’ key. After the Mac OS X Installer has completely initialised, turn on or insert your removable disk. Go to the menu bar, click on ‘Utility’ and choose ‘Restore System From Backup’.
Select your backup source and click on ‘Continue’. You will now be presented with a choice of which Time Machine backup you want restored. Note that the dates and times in this window are presented at the GMT +0000 timezone. You’ll probably want to choose the most recent backup. Now, select a destination for restoration. We can’t help you out here, but this will be the drive that hosts your current OS X installation. Click on ‘Restore’ once you have chosen the destination drives. The installer will then begin restoration.
A good overview of the restoration process can be found here.