It is just a short distance to the west of Old Olny, the door is below a rock outcrop, if you find an old barn you have walked passed it. If you've not found Old Olny then look for it to the East of Clifftop Shacks, or north east of Greener Pastures Disposal site.
SPOILER: no he is in vault 112 in smith Casey garage
Vault 112 is in Casey smiths garage once you activate the electrical switch and you will have the doors into the basement open and then you get into Vault 112 and are spoken to by a robo-brain or whatever, and you go into the machine after you change into the Vault 112 vault suit.
There are 7 vaults as follows: Vault 87 Vault 92 Vault 101 Vault 106 Vault 108 and Vault 112
Yes, if you follow the main storyline you will finally meet him in vault 112.
There are no enimies inside the vault itself but there are a few mole rats in Smith Casey's garage, which you have to go through to get to vault 112
There is many hidden quests in Fallout 3 but i there is one when you reenter the vault. (after you father dies) hang around the vault entrance.
vault 77 doesn't exist in the game.
Just North from Vault 101.
All Vault Tech Vaults in Fallout 3 where made public. You are talking about private shelters that are scattered throughout the Capitol Wasteland.
south-east of vault 92
Yes. Seven vaults exist in Fallout 3. One of them is Vault 101, where your character begins the game. For spoilers as to who or what lives within the remaining vaults, check http://fallout.wikia.com/wiki/Vault .
In Fallout 3 vault 101 is the only Vault still active, every single other vault the people went crazy and then they killed eachother, simply because they wanted to leave the vault so bad because they were trapped in there