How To Bring Back WordPress Post Preview

The latest versions of WordPress (from 2.2 on, I think), removed a feature from the posting interface that showed a preview of the post you were working on. For some bloggers, that feature is very important, as we’d like to track changes in our posts as we work, but the developers did not leave a setting to turn it back on.
Luckilly, adding it back is damn easy. Here’s what you gotta do:

Edit your post.php file. You can use FTP software to get it, or your server control panel, or:
Go to Manage, then Files in your WordPress control panel. Click any file on the right side, then go to the address bar and delete everything after “file=”. Replace it with wp-content/post.php and hit Enter.
Find this link in the file: include(’edit-form-advanced.php’);
Right after it, add this:

?>