I am assuming you just want to rotate your screen for things like emails and texts, since the default diamond keyboard does landscape mode (ie in Opera). You can do like
here to get a app in your start menu to rotate your screen. You can also download a program called AEButton Plus and set a button push to rotate the screen (I use long push volume up). You can also google FlipIT or Gyrator as well. If you want a nice keyboard that works well in landscape, search for Finger Keyboard.