To own two houses at once, first disarm the bomb in Megaton to obtain the key to "My Megaton House". Make your way to Tenpenny Tower, enter the lobby, and use the elevator behind the main desk to get to the penthouse suites. Convince the guard to let you into Tenpenny's suite, then get on the balcony overlooking Capital Wasteland. There will be four doors: two will be boarded up while onedoor will be described as "Empty suite locked-key required". You can still open the door without the key and treat it as your own house, as if you destroyed Megaton. Note: You cannot open the suite from the inside. This is why you need to get into Tenpenny's suite. You can only enter or leave from the balcony.