By the time you are around level 10, give or take a few, you've come the the mission, "Tranquility Lane". If you just follow the main quest, you will take a terrible blow to your karma.

For those of you who are going for a character with a bad karma, good for you. Follow the main quest.

To complete this quest and still maintain a high karma, you will need to find the "Abandoned House" on the street in Tranquility Lane. The Abandoned House is the run down home.
Now to the actual guide. Upon entering the home, you will notice a series of items lying on tables in the room. These items consist of everday items you encounter in the wastes like, a broken pitcher, a gnome, and a radio, but when activated in a certain order, these items unlock a failsafe.

To unlock the failsafe, activate the items in this order: Broken Radio, Glass Pitcher, Garden Gnome, Glass Pitcher, Cinder Block, Garden Gnome, and Empty Bottle.

If you hit them in that order, you will notice to the right of the room, a computer terminal has appeared. Activate it, and hit the first sentence, I believe it says something something... activate Chinese program. (sorry for being sloppy there, but I haven't done this in a while) Before initiating the failsafe, you are required to read about it first. Click the second heading, and just read through it. After that, now you can initiate the Chinese Invasion. Walk outside, and you will notice Chinese soldiers have appeared in the town. They resemble the soldiers in the "Operation Anchorage" dlc.

A door out of Tranquility Lane will appear in the main park in the middle of the map. Simply exit through it.

Now you're done!

I did not make this guide with the intention to become, a sort of, "famous" in the Fallout 3 Steam community. I just wanted to help players who want to maintain a good karma throughout the game.
I doubt this guide will become too popular; I'm sure there are many like it, and some better, on YouTube.

However, if this guide did help, I would extremely apreciatte leaving a comment, and likeing the guide.

That being said, thank you for reading, you guys are awesome. Please forgive any grammatical or spelling errors I made in the guide. Now go make some Deathclaw heads roll!