For the Sparta badge, MAX out flamethrower, after that, spend all remaining money on gunmen. The flamethrower will do damage over time, killing the spartans before they get to the building. The gunmen will help pick off stragglers. I Didn't get hit once.
Some of the jumps are really nasty. There are two boxes in the most inconvenient spot there is at the end of a building. I can't jump them without falling into the hole, but I can't make the jump without running into the trash cans. Arrrgh!