If you Mac or OSX crashes, and yes this can actually happen, you may want to install your Mac using a Time Machine Backup. In order to do a system restore from Time Machine, you need the backup to be a full backup. If any of the system files are missing then the restore will fail. In general it's advised to install Snow Leopard from the DVD's and then use Time Machine to copy files back to your Mac. Time Machine usually includes your user folder and programs installed on the system.
The following procedure can also be used after installing a new hard drive in your Mac. Remember that you can replace the hard drive without burning your warranty!
- Boot from the OSX system DVD that came with your Mac.
- Let the system copy necessary files and once ready choose your language.
- On the main setup screen choose Disk Utility from the Utilities menu.
- Select the hard drive and click Partition.
- In the partition menu select only 1 partition.
- Click on options and choose GUID Partition Table.
- Make sure that MAC OSX Extended (Journaled) is selected in Format!
- Click OK and then Apply.
- Choose Yes to whatever pops up.
- When formatting is finished you can close the Disk Utility Window.
- Once the Welcome Screen re-appears, click Back! (this is due to a bug in the installer preventing it from identifying the newly formatted hard drive).
- Select language once again and click next.
- On the Welcome Screen click Utilities and select Restore System From Backup.
- Let the process finish itself. A simple restore can take for one to several hours depending on how much data is contained in the backup.