You Can Turn 32-bit Vista into 64-bit Vista
Vista is the first client platform that features both the x86 and x64 flavors simultaneously, on the market since the moment of launch. Although Microsoft delivers the operating system on a single DVD, the media only contains either all the 32-bit editions, or all the 64-bit SKUs, but not all of them.
In this context, jumping from the 32-bit version of the platform to the 64-bit one is not as streamlined a process as it might seem. The Windows Vista Anytime Upgrade options do allow end users to easily jump from a low end edition of Vista up the scale toward and to the Ultimate edition, but this is valid only from one 32-bit SKU to another 32-bit SKU. Respectively from a 64-bit variant to a more feature-rich 64-bit variant of Vista. The move from 32-bit to 64-bit is not supported by Microsoft, whether it is referring to a shift between SKUs, or from one x86 edition to its 64-bit counterpart.