It's changeable in the options. You can even set it upside-down. XD
TATE is commonly used for vertical shmups. Makes the screen bigger and clearer. Looks better on a 4:3 monitor though IMO (cuts off the extra top and bottom borders).
I personally want to set-up my gaming rig this way now: http://www.youtube.com/watch?v=HQGxYLxG8Yw XD