Three ways to install
When you start the upgrade process, you’ll get to choose one of three ways to install Tiger on your Mac.
Simple Upgrade: This option upgrades all the important components of your old system software while preserving all your personal files and most settings. Could it be any easier?
Archive and Install: This option saves your existing system files in a special archive, then installs Tiger. You can choose to automatically import your user information and settings into Tiger so you don’t have to reconfigure your printers, Mail and other applications.
Erase and Install: This method completely erases the destination volume, then installs a new copy of Mac OS X. You’ll have to copy all your files and re-enter all your account settings.