If you have problems removing/upgrading .NET the following may be useful to remove a broken installation of .NET.

http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx

Note that it should not be used to remove the version of .NET that came with the OS and obviously you should try to remove via Add/Remove Programs first.  Also check that the version you want to remove is not in use by any of the sites in IIS first.

The .NET Framework cleanup tool supports removing the following products:

· .NET Framework - All Versions

· .NET Framework - All Versions (Tablet PC and Media Center)

· .NET Framework - All Versions (Windows Server 2003)

· .NET Framework - All Versions (Windows Vista and Windows Server 2008)

· .NET Framework 1.0

· .NET Framework 1.1

· .NET Framework 2.0

· .NET Framework 3.0

· .NET Framework 3.5

· .NET Framework 4