This week, Microsoft is releasing another series of test (aka "fake") updates for Windows 7 (Redmond released test updates for Windows 7 Beta 1 back in February). As with the test updates for Windows 7 Beta 1, the test updates for Windows 7 RC are designed to make sure that the Windows 7 update mechanism is working properly.
The release started Tuesday, so you may already have some test updates set to arrive on your system. Most will install automatically, but KB970420 must be installed manually through Windows Update. According to PC World, as many as ten test updates may be sent. Look for the phrase "Test Update" when you review Windows Update history.
Speaking of Windows Update and Windows 7 RC, 32-bit users should make sure they've installed the update referred to in KB970789, released late last week. This fixes a major show-stopping bug affecting folders created under the root folder and the applications that try to access them.