io.sockets.on 'undefined' (node.js + socket.io)

I'm a beginner at node.js and socket.io trying to get a server running so I can push updates to clients. I'm attempting to follow this tutorial: http://danielnill.com/nodejs-tutorial-with-socketio/

I have node.js installed and confirmed with the command "node -v" on my VPS running Centos 6.4. I've ran the command "npm install socket.io" in the directory I'm running my server.js file. However, using "io.sockets.on" results in a "TypeError: undefined is not a function" error in the console.

server.js file:

var http = require('http');
var url = require('url');
var fs = require('fs');
var io = require('socket.io');

var server = http.createServer(function(request, response){
console.log('Connection started...');

switch(path){
    case '/':
        response.writeHead(200, {'Content-Type': 'text/html'});
        response.write('Hello World');
        break;
    case '/socket.html':
        var data = fs.readFileSync(__dirname + path);
        response.writeHead(200, {'Content-Type': 'text/html'});
        response.write(data);
        break;
    default:
        response.writeHead(404);
        response.write('ERROR 404');
        break;
}
  response.end();
 });

 server.listen(8000);

 io.listen(server);

 io.sockets.on('connection', function (socket) {
     console.log('hello world');
 });

client html:

<html>
<head>
    <script src='/socket.io/socket.io.js'></script>
</head>
<body>
    <script>
        var socket = io.connect();
        io.sockets.on('connection', function(socket){
socket.emit('message', {'message': 'hello world'});
 });
    </script>

    This is our socket.html file
</body>

All code works fine without the socket.io components, so I know node.js is working properly. Is something wrong with my socket.io installation or am I missing something very obvious?

Thanks