Hi there,
For your first point it sounds like your screen resolution is not in a 16 : 9 ratio. Was your old monitor 4:3 ?
Have you got a PC? You should be able to right click on the desktop and in the settings tab adjust your screen resolution so that it has a 16 : 9 ratio. Ie, 1600 by 900 pixels.
This will mean that your models and indeed anything on your monitor will be displayed correctly. You may want to test it with a perfect circle, if it appears elliptical, you’ve gone wrong some where…!
For the other issue I think that is covered in the general tips and tricks section of the on line wiki:
http://www.pixologic.com/docs/index.php/Tips_and_Tricks#ZBrush_launches_with_the_window_off_center_on_the_screen_or_not_using_the_whole_screen._How_to_fix_it.3F
Hope that helps!
James