Clean Install Types
To perform a clean install on a drive that has an existing Mac OS X installation, you have two primary options: archive and install or erase and install.
Erase and install does exactly what it sounds like: It reformats (erases) the hard drive or partition and then installs a clean copy of Leopard on the now-empty drive.
Archive and install, on the other hand, does not erase anything. Instead it creates a folder called Archive and copies the Mac OS X System, Library, and Application folders to it (along with the Unix system directories that are normally invisible).
User home folders are preserved, but user accounts are not (as they are stored with the Mac OS X system files). After performing an archive and install, you will still need to go through the Leopard setup assistant, create user accounts, and configure your various system and application preferences.
However, you will be able to access any previously installed applications as well as their support and preferences files (and any system-level files, such as fonts, screensavers, or System Preferences pane), though you they will have to be copied to the appropriate locations from the archive.
Archive and install is a good halfway point between a complete clean install and an upgrade because it doesn’t require you to erase the hard drive, thus preserving all your existing files, but it also ensures that your Leopard installation is completely fresh.
If you want to have the option of archive and install but maintain your existing user accounts, there is a checkbox to preserve users and network settings when performing an archive and install. This option performs the archive and install process, giving you a completely fresh Leopard install, but it also copies your existing network settings and user accounts into the new Leopard installation.
Preserving your user account information and network settings means that you don’t need to go through the Leopard setup assistant.
For many users this is a win-win situation because it is a fresh install of Leopard, but at the same time doesn’t require much setup afterward. Also because user home folders are preserved along with accounts, most user preferences should transfer fine.
There are only a couple of concerns with this approach. One is if you have anything unusual in your existing user account structure, as mentioned in the upgrade section, which for most Macs is not particularly likely.
The other more-probable issue is if you have any Mac OS X or application add-ons stored in the Library folder inside your home folder that might conflict with Leopard.
You can, however, sidestep this problem by checking for third-party items in your Library folder before installation and moving them or by removing them if you experience problems.
If you choose to archive and install (regardless of whether you preserve users and network settings), keep in mind that you will essentially have two Mac OS X versions on your hard drive, which can take up quite a lot of space.
After installation, you should determine what, if anything, from the archive folder you need/want to transfer to Leopard, test those files to be sure there are no problems, and then discard any unneeded files.