I love how the tank's shots, because they are still attached to the tank, can be turned around to hit the other player!
As for the scorekeeping, you could put 2 3D text objects in the center and when a player dies, the text object updates its text with "1P <number of points> Points"
I made a quick example of it (seen in the picture below)
==============Some of my Games and Ideas===========
Sky Warrior: http://www.alice.org/community/showthread.php?t=6291
Health Bars: http://www.alice.org/community/showthread.php?p=36968#post36968
Sky Warrior: Dual Force: http://www.alice.org/community/showthread.php?t=7174
Want to make your own space game? http://www.alice.org/community/showthread.php?t=6389