When you talk to the Sheriff of Megaton, ask about disarming the bomb.

Find a Mister Burke at the bar when you look for your dad and he'll ask you to RIG the bomb.

Choose to disarm you get a place you call home at Megaton when you go back to talk to the Sheriff or his son Harden.

If you choose to RIG the bomb do it when your further down the line of the game or it's going to be difficult trying to get past raiders and creatures unharmed.

When you do the Tenpenny Tower will be marked on your map and you go there.

Once there find Mister Burle and Tenpenny on the roof with a detonator and you'll have the honor of destroying the city of Meagton, receiving major bad Karma and your very own Tenpenny Suite but no more Megaton.

The only survivor from the explosion is Moira Brown, the crazy shopkeeper of Craterside Supplies.