The latest test version is available in English, German and Japanese for 32-bit and 64-bit systems.
Microsoft plans to issue a limited number of product activation keys, but a spokesman was unable to specify how many.
The software giant anticipates that five million people will have a chance to evaluate the software. This number includes roughly 500,000 IT professionals and developers who received access to the software on 1 September.
Vista Release Candidate 1 will expire on 1 June 2007, at which time users will be required to install the final version of Windows Vista or downgrade to Windows XP.
Microsoft warned that Release Candidate 1 should not be used in a production environment or on the primary computer at home.
Users also might not be able to upgrade the Windows Vista RC1 installation to the final commercial version of the operating system.
The software is available for download from the Microsoft Vista website or testers can order a DVD at a small fee to cover production and shipping costs.
IBM and Technical University of Munich team demonstrate how Shor's algorithm, which can't be cracked by conventional computers, can be solved quickly with quantum computing
Hubble Space Telescope finds superflares from young red dwarfs could strip away planetary atmosphere
Younger stars are 100 to 1,000 times more energetic than when they're older
Two of the big four supermarkets will use the system to control sales of restricted products
PUBG news and updates: November's Update #23 to bring new Skorpion pistol and changes to blue zone visibility
Genuinely useful side-arm coming to PUBG in Update #23