title: Download an save an image file on HDD with Cocoa
body: <p>I'm building a program, and I'm quite confident using Objective-C, but I don't know how to programmatically download a file from the web and copy it on the hard drive.
  I started with :</p>
  
  <pre><code>NSString url = @"http://spiritofpolo.com/images/logo.png";
  NSData* data = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
  </code></pre>
  
  <p>But then I don't know what to do with the data... that sucks, no ;)
  Can somebody help?</p>