Upgrading your copy of Windows XP to one of the editions of Windows Vista is not as simple as you might first think. Vista is no Mac OS X after all, so the upgrade paths tend to be a tad more complex. As far as upgrading from Windows XP to Windows Vista is concerned, there are a few things that you need to know before you proceed with the process.
For moving to Windows Vista, Microsoft delivers two standard options: either a clean install or an upgrade. The advantage of an upgrade is that you get to keep all your files, settings, and programs. Upgrading a 64-bit version of XP to a 60bit edition of Vista is not possible. You will have to clean install Vista.
However, with the 32-bit editions, your options are more varied. I have also included a set of images at the bottom of this article that will provide a graphic reference to the upgrade paths available between 32-bit XP and Vista. Just click on each image in order to access a readable variant.
First of all, you have to consider the XP options available. Windows XP Home Edition, Windows XP Professional (32-bit), Windows XP Professional x64 Edition, Windows XP Tablet PC Edition, Windows XP Media Center 2002 Edition, Windows XP Media Center 2004 Edition and Windows XP Media Center 2005 Edition, all have different upgrade paths to Windows Vista. Still, all XP editions share a common characteristic. None of them can upgrade to a 64-bit edition of Vista. Either you start from a 32-bit or a 64-bit Windows XP, you will have to clean install a x64 version of Vista.
Windows XP Home Edition can upgrade to Windows Vista (32-bit) Home Basic, Home Premium, Business, or Ultimate.
Windows XP Professional can upgrade to Windows Vista (32-bit) Business, or Ultimate.
Windows XP Tablet PC Edition can upgrade to Windows Vista (32-bit) Business, or Ultimate.
Windows XP Media Center Edition 2004 or Windows XP Media Center Edition 2005 can upgrade to Windows Vista (32-bit) Premium or Ultimate.
Source:→ softpediaMicrosoft, Windows Vista, Windows XP, Upgrade, Upgradation, Tips, Tweaks, knowledgebase