YOU GET TO PLAY RISK AT SCHOOL? Why dosn't my class get to do anything cool like that?
Anyway, I'd say build up a fall back point that you can turtle in if something goes horribly wrong. That way you can regroup and slowly but surely reenter the world stage.
For the alliance bit, can't give you any help there. Never used diplomacy anyway. Hard to do for two person games.
Best territory/country? If you want to attack nonstop (bad idea btw. Don't do it. There is no measure of time in existance that will describe how fast you will die) Southern, Eastern, or Northern Europe, or Middle East. If you want to play attritionally (you wear out the other players) Pick Siam or Indonesia and build up in Australia, and let the other players break up their armies on your solid defenses. Then, when everybody's weak, jump out and kill everyone you can without stretching yourself too thin.
Let us know how it goes, btw.