I wrote a couple of macro routines to do the same for Visual C++ editor. When you select a block of code and click on CommentBlock toolbar button, the selected text will be commented out with '//'. When you click on UncommentBlock toolbar button, the selected text will be uncommented if it was commented out with '//'.
To install the macro file, download it to your Visual Studio macro directory. This is usually C:\Program Files\Microsoft Visual Studio\Common\MSDev98\Macros. From the Visual C++ editor, simply create two toolbar. Set each of them up to to run these macros: CommentBlock and UncommentBlock.