You’ll want to use the add_members script to do what you need. Note that your csv needs to be of the format:

"Firstname Lastname" email@example.com

$ /usr/lib/mailman/bin/add_members -h

/usr/lib/mailman/bin/add_members
Add members to a list from the command line.

Usage:
    add_members [options] listname

Options:

    --regular-members-file=file
    -r file
        A file containing addresses of the members to be added, one
        address per line.  This list of people become non-digest
        members.  If file is `-', read addresses from stdin.  Note that
        -n/--non-digest-members-file are deprecated synonyms for this option.

    --digest-members-file=file
    -d file
        Similar to above, but these people become digest members.

    --welcome-msg=<y|n>
    -w <y|n>
        Set whether or not to send the list members a welcome message,
        overriding whatever the list's `send_welcome_msg' setting is.

    --admin-notify=<y|n>
    -a <y|n>
        Set whether or not to send the list administrators a notification on
        the success/failure of these subscriptions, overriding whatever the
        list's `admin_notify_mchanges' setting is.

    --help
    -h
        Print this help message and exit.

    listname
        The name of the Mailman list you are adding members to.  It must
        already exist.

You must supply at least one of -r and -d options.  At most one of the
files can be `-'.

For example, “ls /usr/local/mailman/lists | cat > lists.txt” is exactly equivalent to “ls /usr/local/mailman/lists > lists.txt”.

If you install Cygwin on your Windows XP system (see cygwin.com) you’ll have all that you need (including Python) to run the scripts above. [I just discovered this -- won't tell you how long I've been looking for something I could script locally. Thanks, folks.]