Fallout: New Vegas Walkthrough - Boulder City Showdown
Boulder City Showdown is a side quest that you'll run right into when you find the Great Khans in Boulder City for the main quest. If you want to help the Great Khans, the NCR or just stay neutral, then find out the different options for completing the quest below.
Boulder City Showdown - Introduction
You will literally run right into this quest as you work on the main quest. When you go into Boulder City, you'll find a group of NCR troopers surrounding the ruined section of the city. If you talk to Lt. Monroe, he'll explain that a group of Great Khans fired on some troopers and took a patrol hostage. You need to talk to the Great Khans anyway, so volunteer to be the negotiator.
As soon as you talk to Jessup you'll find out about Benny's betrayal, so that takes care of the main quest. You will have to decide how you want the showdown to play out though.
Note that, as odd as it may feel, helping the Great Khans, or at least remaining neutral will be much more helpful for the NCR quests in the future when it comes time to get the Great Khans to pick sides in the war.
Boulder City Showdown - Battle
To get this out of the way, a battle is just as straightforward as you would imagine.
If you want to help the NCR and save the hostages, walk up to the two hostages and their two guards in the building next to the main hideout. Take aim and get a big critical sneak hit on one of the guards, then use VATS to kill the other. The hostages should be safe. Use this position as a sniper's roost and pick off anyone in the streets that comes to fight you. The doorway makes for great cover.
Go into the main hideout with a loaded shotgun or melee weapon and kill Jessup and the few remaining Great Khans inside. Free the hostages by talking to them and then go back and report your success to Lt. Monroe.
If you want to help the Great Khans, just approach the NCR firing line and get off to the side. Sneak and land a critical hit on one of the soldiers, then engage the rest. There should be about five. Try to fall back to a building for cover and just get into a sniper duel with them. Their service rifles are deadly, but half decent armor should negate the bulk of the damage. A melee rush should also be surprisingly useful, since they're all close together at the start. Note that the hostages apparently are tagged as Great Khans (which makes sense, to keep the guards from killing them. Killing the hostages may cause the Great Khans to attack you). Just leave them alone or wait until you're alone. Leave the ruins and kill Lt. Monroe to finish the fight. Report your success to Jessup and he'll retreat through the opening you created.
Boulder City Showdown - Neutral
If you want to keep a good reputation with both sides, then you need to use your Speech skills.
There are a few options, but the best option requires 45 points in Speech. With this, you can convince Jessup to let the hostages go and try to leave peacefully. If you do this, you can run to Lt. Monroe and tell him about the deal. He still has orders to kill the Khans, but he's hesistant. If you question him on what he feels about the deal, he'll admit that it's wrong to backstab them and just let them go without any further checks. There are other options, but there's no reason to use them.
If you pick this option, you'll gain reputation with both the NCR and the Great Khans.