I have previously posted some instructions (here and here) that can be used to verify and attempt to repair the files that ship as a part of the OS on Windows Vista. Since I wrote those posts, I have heard from a few customers who have attempted to use those instructions to repair their .NET Framework 2.0 and 3.0 files and/or Media Center files on Windows Vista, but received error messages from Sfc.exe indicating that some of the repair operations were not successful.
Fortunately, I recently found a Microsoft knowledge base article that provides more details about how to use Sfc.exe on Windows Vista, including steps that can be used to locate error messages and manually fix files that it was unable to repair.
You can find this knowledge base article at http://support.microsoft.com/kb/929833. If you are running into problems with Windows Vista and suspect that some of the OS files may be corrupt or missing, I'd suggest trying out the steps in this knowledge base article to see if they help correct the issues that you are seeing.