Upgrading from Windows XP to Vista
ExtremeTech provides practical advice on upgrading from Windows XP to Vista. Note that some versions of Windows XP will not upgrade to Vista. A table is included to let you know which versions are upgradeable. Upgrading in place (without a clean install) is not possible from Windows 2000 or Windows XP 64. However, you may still get upgrade pricing and do a clean installation.
Apparently, the installation process is quite different than for previous Windows versions. This article has many good tips. It’s definitely worth your time.