This video shows you how to get every single Fallout 3 achievement, almost instantly, with no mods, or hacks. The steps performed are the following:
Install Fallout 3
Sign into your account
Press the ~ button to open the console (It's left of your 1 key and above the TAB button)
Type in "addachievement 01"
Repeat that until you reach "addachievement 53" going up numerically
That's it! You'll have every achievement.
There are no repercussions for doing this, you are not hacking or tricking the system, it's included in the game. It's like using cheats for a video game, except instead of getting a cool gun, you get an achievement.