abort: no username supplied (see "hg help config")

Here is what worked like a charm for me on Windows XP:

Go to the folder 'C:\Program Files\Mercurial\hgrc.d' assuming you have installed Mercurial to'C:\Program Files\Mercurial\'.
You should see a Mercurial.RC file in there.
Copy the file to 'C:\Documents and Settings\ [USERNAME]\'
Rename Mercurial.RC to Mercurial.ini.
Edit the [ui] section like so:

[ui]

; editor used to enter commit logs, etc. Most text editors will work.

editor = notepad

verbose = True

username = [e-mail]