Ok this has been buggin me sense the day this came out.. when you frist leave the vault and walk to mageton there is a little town with burn house and a gas startion on the right hand side there is a burn house but in that burn house on the ground there is a door that is locked that needs a key to open it .. and was wondering if anbody knows were i can get my hands on that key cause i just really want to see whats in side...

You're talking about that basemant in that burned house in Springvale. Yes. Well, if you have Fallout 3: Game Of The Year Edition or simply just have the Broken Steel DLC, in general...you'll be able to have access to this basemant door. After you complete the main quest of Fallout 3(Baby Steps - Take It Back!), go to this location and there will be a man there by the name of Brother Gerard. Upon drinking his holy irradiated water as part of the manifestation of atom's light, he will grant you the key to this door.

It's all apart of the "Holy Water" quest, which is a sidequest from Fallout 3's Broken Steel add-on. Remember, though. You won't be able to access this door/start the "Holy Water" quest until you've completed the main quest of Fallout 3.