- If you are a Windows Vista or Windows Server 2008 user and you are upgrading from IE8 Beta 1 or Beta 2 to IE8 RC1, you are no longer required to manually uninstall earlier IE8 builds. Instead, IE8 RC1 installer will automatically upgrade your machine from the earlier IE8 builds to the latest IE8 build, all with a single reboot.
- There is a new pre-requisite for IE8 RC1 (KB957388). This update supersedes KB943302 and KB957055 and will be automatically installed as part of your RC1 upgrade, as long as you keep “Install the latest updates” checkbox checked. This update addresses known application compatibility issues in Windows Vista and Windows Server 2008 and improves the performance and reliability of IE8.
- All IE8 Beta 1 and Beta 2 users will be offered IE8 RC1 via Windows Update in 25 languages. For Windows XP and Windows Server 2003, the IE language that gets offered via Windows Update will match the base OS language. For Windows Vista and Windows Server 2008, the IE language that gets offered via Windows Update will match the Active Language that the user selected for their account.
Note: If you are running Windows 7 Beta, you will not be able to install IE8 RC1. You will get an error message saying that your operating system is not supported since IE8 already ships in Win7. The IE8 RC1 available from Microsoft Download Center is a standalone upgrade for downlevel version of the OS only: Windows Vista, Windows XP, Windows Server 2008 and Window Server 2003.
You can find more details and steps to upgrade here.