I have set the %HOME% environment variable on my Windows installation.
In that folder I have put a file called _netrc. Inside that file I have:
machi
Assuming you did everything that was described in this answer and you set the right location for your %HOME% environment variable (confirm this with an echo %HOME% and check that in that location there's a _netrc file), there must something be wrong in the usage of your repository.
The URL to clone a Google Code repository is https://user.googlecode.com/svn/trunk (see this Google link for that).
So, you have to do a
git svn clone https://user.googlecode.com/svn/trunk
in order to import your Google repository.
I've been bashing my brains against this one too and I have a solution different from those posted.
Ensure that your _netrc file is Ascii encoded. If using ECHO redirecting to a file on standard out, Windows uses the UCS-2 LE BOM file format. Some other apps might also have a different default from Ascii.
So, if creating this file via script, use Set-Content -Encoding Ascii rather than a STOUT redirect. If creating this file via notepad++ or vim, ensure the encoding is set to ASCII.