In the first room there is a giant robot swinging his arms on the left side...you need to aim at the target on his Left arm..the second arm. Each hit there will get you 100,000 pts.
In the second room there is a volcano on the right side in the back. You need to aim for the top target on the volcano, that will give you 25,000 per hit.
Then there is a giant Zurg in a ship on the right in the next room...you have to aim for the bottom target on the ship, directly under Zurg...that is also 100,000 per hit.
There's one more in the video room, but it's much harder to hit. The first 3 should get yo maxed out.
If you want to see it play by play, check out this link:
http://www.youtube.com/watch?v=1lXv7-906ow
Good Luck space rangers.