After you've made the decision to install XP, you're faced with two installation options: installing or upgrading.
When performing a clean install, you place a brand new copy of XP into the destination partition, completely wiping out any versions of Windows (or any other files and folders, for that matter) currently residing there. This slash-and-burn technique is one of the choices you make from the Setup dialog boxes, and it can be selected when starting XP Setup from within previous Windows versions. If installing XP on a new computer or new primary hard drive for an old computer, you will of course perform a clean install.
The easiest way to perform a clean install is to boot the Windows installation CD. You may need to adjust the BIOS settings of the computer first, but most computers that meet the minimum hardware requirements for Windows XP can be set to boot from the CD. Because a clean install starts with a freshly formatted partition and thus wipes out any data on that partition, you need to make sure that a backup exists if you want to avoid losing old data.
Upgrade Over an Existing Windows Version
You can update to XP from nearly any currently running version of Windows, including 98, Me, NT 4 (Service Pack 6 or higher must be installed), and 2000 Professional. There are exceptions: you can't upgrade from Windows 95 or 3.1 (although the hardware on such computers is not likely to support XP anyway).
The advantage of upgrading is that all your current configuration settings are kept intact. You have a new OS, but you retain the old Desktop, Start Menu contents, My Documents contents, Internet Explorer Favorites, and so onyour environment doesn't change. To perform an upgrade, just insert the Windows CD and choose Upgrade in the Setup drop-down menu shown in Figure 2-2.
Figure 2-2. Clean install or upgrade?
And, just so there's no confusion, you can still choose XP for your OS if you're running a Pentium II with Windows 95, for example. You will just have to perform a clean install, resulting in either a multiboot configuration or a clean slate of Windows XP.
All three installation options are available with the various methods of performing an attended installation. One of the more common methods is to insert the XP CD-ROM from your current operating system.