Migration: Make the Move to Vista
We recommend a clean install of Vista, but we know that many folks prefer to upgrade from XP to avoid having to reinstall their apps, files, and settings. In most cases you can switch from XP to Vista without preparing at all, though we recommend that you back up your files in case something goes wrong.
An upgrade merely installs Vista directly over XP, retaining all of your applications, files, user accounts, and other settings. For safety's sake, before you do an in-place installation, back up all your files, just in case something goes wrong. Conversely, a clean install wipes out all traces of XP and of your applications, files, settings, and user accounts, deleting everything from your hard disk (including all the problematic Registry entries your system has accumulated) once the fresh copy of Vista is in place. Windows Easy Transfer, Vista's version of XP's Files and Settings Transfer Wizard, lets you move your settings, files, and apps to a clean Vista install via a direct cable connection or over a network.
Why do a clean install instead of an in-place upgrade? Not every version of XP can be upgraded to every version of Vista. For example, upgrading from XP Professional to Vista Home Premium requires a clean install. At Microsoft's site you can view XP and Windows 2000 upgrade options.
One final note: Before upgrading from XP, confirm that your PC can run Vista by downloading and running Microsoft's Windows Vista Upgrade Advisor. It will tell you which versions of Vista your system can run, and it will make recommendations for hardware upgrades if it determines that your PC isn't up to snuff.