Hi,
Maybe your .NET installation is corrupted (as indicated in the error messages you pasted above). Look at the following blog, download, install and run the .NET framework cleanup tool (following the instructions), then re-install Visual Studio and BizTalk, and hopefully that resolves your issue(s):
http://blogs.msdn.com/b/astebner/archive/2006/05/30/611355.aspx
Best,
Daniel.