One area that I have been diligently researching for several days is the issue of Windows Vista and which versions are 32 bit, 64 bit or both. Microsoft has neglected to document this up front. Yesterday I was finally able to get some definitive answers to this mystery.
Vista is available in both 32-bit and 64-bit versions, but some are easier to obtail than others.
The following Vista versions are available as 32 bit programs when purchased retail.
Home Basic
Home Premium
Business
At this link you can upgrade your 32-bit Vista to 64 for a nominal fee.
http://www.microsoft.com/windows/products/windowsvista/editions/64bit.mspx
Windows Vista Ultimate has both 32 & 64 bit versions on the installation DVD.
Another nugget on this page is that all 32 bit versions of Vista are limited to 4 gigabytes of RAM while 64 bit OS can support up to 128 GB of RAM depending of which version that you are running.
32-bit versions of Vista will support 16-bit applications but the 64-bit OS won’t unless you are running Microsoft Virtual Machine 2007, which will be a free download later in the year. Virtual Machine will allow 64-bit operating system to operate 16-bit programs in a virtual environment running older versions of Windows. Virtual Machine 2004 is available for download now.
Also Microsoft is offering an upgrade special that can save you money over the retail prices. If you buy either full or upgrade version of Vista Ultimate, then you can also purchase license for two copies of Vista Home Premium for $49.99 each. This is simply a key to use same DVD that you already purchased to install the operating system on additional computers. See the link below for details.
http://www.microsoft.com/windows/products/windowsvista/buyorupgrade/familydiscount.mspx