Unlike Windows XP, it is fairly easy to move between versions of Windows Vista. If you have a copy of Home Basic, for example, you can upgrade to Home Premium or Ultimate using a tool called Windows Anytime Upgrade — go to the Start menu and type anytime in the Search box to find it. Anytime upgrade allows you to order an upgrade online, and Microsoft will send you a disc in the post. The prices aren’t particularly keen, though: moving from Home Basic to Home Premium costs over approximately $50, even though the difference in online price between the two boxed versions is closer to approximately $20.
Anytime Upgrade is worth considering if you bought a computer with Vista pre-installed and want a better version, but otherwise we’d strongly recommend checking out the features you want and picking the right version first time — you stand to save money by doing so.