Instructions
Play through the first part of "Fallout 3" as normal. The game starts with your character as a baby, followed by your character around age 9, and finally with your character around age 16. Follow the directions on screen to complete objectives in the early part of the game, allowing you to reach the end of the "Vault 101" segment.
Kill all the guards during the uprising. The reason your character is supposed to leave Vault 101 is because he is being chased by guards throughout the area. Instead of running away and continuing with the game's story, use your weapons to kill all the guards. When a guard sees you, he will immediately open fire; when you no longer are being shot at, you've killed all the guards.
Do not complete the last objective of this area of the game. The final objective of this area is that you need to find the password to a computer so you can open the gate to Vault 101 and leave. With all the guards dead, you now can stay in Vault 101 and talk to friends, family and even childhood enemies without ever leaving and venturing out into the Capital Wasteland.