In
http://tug.org/texlive/svn/setup.html
I see this:
$ svn co svn://username:password@tug.org/texlive/trunk .
For me, on a GNU/Linux box, this has failed. I had to say
$ svn co svn://username@tug.org/texlive/trunk .
and there was no prompt for a password.
Werner