I have been having trouble installing Nuget on my new Windows 7 box.
The first version that I got using the ASP.Net MVC installer was version 1.4
The upgrade tool did continually failed with an error about mismatched checksums.
You need to run visual studio as Administrator to be allowed to uninstall NuGet.
Having uninstalled 1.4 then I was able to install the latest and greatest version (currently 1.6).