Hi,
I was getting the following error when trying to install MVC 3 on my Visual Studio 2010 ultimate installation. It happened in the initial part of the install. After some web searching I managed to find a solution that worked so I thought I would post the link to the blog post that helped.
http://blog.williamhilsum.com/2011/03/error-0x80070643-installing-aspnet-mvc.htm
Look for the second update on the page and follow those instructions to make it work. I hope Microsoft will fix this and re-release the installer.
Jas
VB Magic 