A new feature of WordPress introduced in version 2.6 is revision control for posts. By default this feature is turned on, and there is no obvious way to turn it off if you want. There is nothing in the Admin menu that lets you turn off post revisions.

If you want to turn it off, you need to download your wp-config.php file from your server via FTP so you can edit it. Or, if you have direct access to your server via ssh, you can edit it directly. Either way, once you access to your wp-config.php file, edit it and add the following:

define('WP_POST_REVISIONS', false);

you'll want to put this right after the existing line in the file that reads:

define ('WPLANG', '');

Once you are done, save the file. If you FTP'd the file from a server, you'll need to FTP it back up to the server. Once you do this the WordPress post revision feature should be turned off.