I'm afraid there is no real way to change this. You'll know, of course, that the configuration of the Mail window changes automatically when the iPad is moved from portrait to landscape mode, but there's no way for the user to influence it any further. Having said that, though, if you're using the newer IMAP mail protocol - as opposed to the older POP - you can set up new folders for mail on your iPad if you first establish them on your email server.
Tim
Scotland