If you have a prior version of SP1 beta installed, you must uninstall it prior to installing SP1 RC. Microsoft does not recommend installing this software on primary or mission critical systems.
Windows Vista SP1 Release Candidate is time-limited software. Support is through self-help and peer support via the Windows Vista SP1 forum and FAQ page.
You can now download the update from here, though the advice to wait until your PC does it automatically is good advice for everyone except advanced users.
-------------------- Andy Shaw - Technical and Reviews Editor
Web User