Download and run this:
http://www.microsoft.com/downloads/details.aspx?FamilyId=E6E1C3DF-A74F-4207-8586-711EBE331CDC&displaylang=enDuring the setup, deselect everything, then select just the .NET Development Tools.
Finish the install.
Corflags will be located in: C:\Program Files\Microsoft SDKs\Windows\v6.1\Bin