You're going to have to be more specific than that. There are lots of hidden doors in Fallout 3.
Yes, the character known as Dogmeat, who was originally in the first Fallout game and can be a companion in Fallout 3, is also in Fallout 2. There is a hidden room in Junktown in Fallout 2 inside the Cafe of Broken Dreams, where you'll find him.
Do you mean the door in the cave? If so you have to have the crown from the temple on the third island to open it. The hidden Lagoon behind it I think.
Behind Closed Doors - 1958 was released on: USA: 2 October 1958
Fatherhood - 2004 Behind Open Doors 2-14 was released on: USA: 2005
Arresting Design - 2003 Behind Closed Doors 2-25 was released on: USA: 2004
Washington Behind Closed Doors - 1977 Part 2 1-2 was released on: USA: 7 September 1977
Behind Closed Doors - 1958 Flight to Freedom 1-2 was released on: USA: 9 October 1958
Storage Hunters - 2011 Behind Closed Doors 3-2 was released on: USA: 16 June 2013
no, fallout 2 is for pc.
All American Handyman - 2010 Behind Closed Doors 2-3 was released on: USA: 18 September 2011
That's Life - 2000 Behind Closed Doors 2-14 was released on: USA: 2002 Germany: 29 January 2005
fallout 1 doesnt, since the game ends fallout 2 does