Win32::AuthenticateUser is for impersonating someone else when you are already running on a machine. Your description makes me think you are instead trying to remotely authenticate to a server, which can be done like so:

use Win32::NetResource qw( AddConnection CancelConnection );
# ...
    my $mach= "www.microsoft.com";
    my $username= "microsoft\\administrator";
    my $password= "b1gd0g";
    my $netResource= "\\\\$mach\\IPC\$";
    if(  ! AddConnection(
            { Scope=>0, Type=>0, DisplayType=>0, Usage=>0,
              LocalName=>"", RemoteName=>$netResource,
              Comment=>"", Provider=>"" },
            $password, $username, 0 )
    ) {
        warn "\nCan't connect to $mach: $^E\n";
        return;
    }
[download]

which shows some room for improvement of the Win32::NetResource module. (:

        - tye (but my friends call me "Tye")