LEVEL 5 in the ALIEN campaign: Here's a summery in 10 simple steps. You can use the cheat to make it easier, but you can also do it my way.
1: Don't release any aliens. Use the one the game starts with (the warrior)
2: Don't try to fight the marines (run past them)
3: Find the room with the eggs, and open the one with the Praetorian eggs only!!!!!
4: Now defend the facehuggers with your life, and create a queen.
5: Use the aliens to kill off some marines in order to create more hosts and hive-points. (note: using the Queen helps)
6: Create Eggsack, then upgrade the Preatorians
7: Create as many Ravegers as you can to defend the hive (about 3)
8: Make sure you do not release any other aliens before the Queen lays 45/45 eggs and aliens. (this is the boring part)
9: Now release all the other cells containing aliens or eggs without killing the lieutenants!
10: You now have 100 aliens!