Microsoft has released the first release candidate version of their new Operating System Windows Vista that is available for anyone to download (not just those in the tester programs). Both the 32 bit and the 64 bit versions are available for download on the website.
Once downloaded you will need to burn the ISO to a DVD disk before you can install it.

It is expected that Microsoft will release one more release candiate before the operating system is released officially.

[ Download Link ]