A number of points here:
Firstly, _emacs.d is not a default file name for your init file, ie emacs will not load it automatically. Try ~/.emacs.d/init.el, or ~/.emacs instead.
Secondly, Windows 7 has a feature where it prevents programs from writing to certain system directories, but for backwards compatibility for the many old programs that do this, rather than causing them to fail, it silently redirects the write elsewhere, in an application specific directory. C:\ is one of those directories, so setting your HOME to point there is asking for trouble.
Thirdly, see the other response about backslash being an escape character in Lisp strings.