Windows Vista is a Microsoft Operative System, and cannot be
downloaded, it can only be purchased, as it must be installed using a
valid license number that can only be found on a genuine Microsoft
certificate of authenticity.
The Operative system is the main resident software to manage computer resource and interface with the user.
Once installed, the operative system will allow the user to use a
computer. A computer without an operative system cannot be used.
Other examples of modern operative systems are: Windows 98, windows XP, Windows 7, Mac OS, Linux.
Microsoft, that made Vista, does not sell the software directly. Vista
can only be purchased from third party distributors. Here an example: purchase vista.
For this reasons you will not find any Vista download available from Microsoft.
Different versions of Vista where made available for download for
testing purpose. This will allow you the download of the full Vista
installer file, that must be recorded onto CD after downloading.
Here a download:Windows Vista Download - Softpedia.
The file available on the link above will still not be enough to
install Vista if you do not have a valid version of Vista purchased or
installed before on the computer. You will still be asked for a valid
installation key during setup. If your computer is licensed for Vista,
the key will be printer on a sticker located on the computer. The
installation key is composed by 5 groups of five characters codes, like
in this example: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx.
If you have no valid installation key, then you will need to purchase a genuine Windows Vista.
If you decide to upgrade to Vista you can check if you computer can support Microsoft Vista by using the Windows Vista Upgrade Adviso
If you instead have Vista already installed, and you do not need Vista installer disk, but you only need to download Vista updates, you can use the following links:Windows Vista home pageMicrosoft Windows Update
Microsoft Download Center