On Tuesday, Microsoft reminded users that prerelease versions of Windows Vista will expire at the end of May. Users running Vista Beta 2, Vista RC1, or Vista RC2 will begin receiving warning messages about the expiration on May 18, and the prerelease versions will expire on May 31, after which users will have only limited access to their data.

"To avoid work disruption and loss of data, we strongly recommend that customers running any of these pre-release versions of Windows Vista migrate their PCs to the final version of Windows Vista prior to May 31," Microsoft noted in its Windows Vista blog. "After May 31, customers who continue to use pre-release versions of Windows Vista will be able to log in for two-hour sessions to retrieve data. After two hours of use, the PC will automatically reboot without providing the opportunity to save data. The opportunity to log in normally for these two-hour sessions will be available only until August 28, 2007."

Microsoft said users can purchase an upgrade version of Vista and upgrade in-place or perform a clean install of all mainstream Vista versions, including Vista Home Basic, Vista Home Premium, Vista Business, and Vista Ultimate. However, users who choose to upgrade in-place will need to do so from a compatible version. For example, you can't upgrade Vista Business RC1 to Vista Home Basic.