Just something that works for most people, not sure what drivers are doing this. But on my home pc's and my laptop I can rotate my screen in my configuration of videodrivers.

Try pressing CTRL + ALT + arrow key (down, up, left or right) : ) Hope it works for you : )

focus is a hidden target you can set by using the command /focus, after that you can use it in a macro to target the focus you have set.

macro 1: (use when targetting something)
/focus

macro 2: (use to nuke focus)
/target focus
/cast spell

Mouseover is something that uses your mousepointer in WoW to target, so if you move your mouse over unitframes (player frame, target frame, party frames or ingame models (npc's) and such).

An easy test would be to make a macro
/wave [target=mouseover]

bind this macro to a key (put it on your actionbar that you can access by pressing a key on your keyboard)
move your mouse over someone on your screen or one of your partyframes and press the keybinding you associated with the mouseover macro.

After trying the above you should understand what the difference is between focus and mouseover.

Goodluck!