Cause:
SP1 for Windows 2008 R2 already includes the fixes available in KB976462. The installer does not detect that the required fix is already there and tries to install it again which fails.
Resolution:
Run the prerequisite installer a second time. The second time it should recognize that an equivalent fix has already been installed and not try to reinstall it.
More:
http://support.microsoft.com/kb/2581903
Alternatively:
http://angler.wordpress.com/2012/01/12/sharepoint-2010-prerequisites-installer-error-kb976462-could-not-be-installed/
http://archive.msdn.microsoft.com/KB976462/Release/ProjectReleases.aspx?ReleaseId=4317
