Is there a way to go back inside Vault 101 once you leave it in the beginning of the game? I got the pass codes to re-enter it, but when I went back it said the password was changed. How do I find out this password?
At the risk of being a bit spoilery, just to give you a heads-up, the access you get later in the game depends heavily on your decision in the related quest. If you complete the scenario one way, you will be locked out of there forever, in which case you should make sure you have absolutely everything you want out of there before you exit (don't forget to pinch the bobblehead from your father's office). However, if you complete it the other way, it will remain open to you at all times. I just won't say what the quest involves, or which way triggers which outcome. One thing I will say, though; I had a hell of a lot of fun doing that quest as a bad guy.
SPOILERS!!! Servo, I finally got access and instead of killing the Overseer I managed to talk him into handing over the reigns to Amata. In turn she ended up thanking me, but kicking me out and closing the vault. I was like WTF??? I thought being nice would get me access to the Vault all the time. Should I have killed the overseer or messed up that reactor system instead?
Yeah, on my first playthrough, I also thought playing nice would get me permanent access. Turns out there's only two ways to keep the vault open... 1. Sabotage the Vault. Everyone will be evacuated, and the vault will be left open to the elements. 2. The way I did it on my second playthrough; kill everyone. You'll fail the quest, but the vault will stay open. Just beware of Radroach infestations.
It's really too bad that Broken Steel didn't really add anything to the Vault 101 storyline. That seems like the one place that you'd like to have some kind of follow up from anyway.
Dangit! I am going to reload from a save before it and go back and do it again. I thought if I left them alive I would get to encounter them on future missions in the wasteland.
If you sabotage the vault and everyone has to be evacuated, you will randomly encounter V101 characters in the wasteland (asuming you haven't killed them). The vault stays open, too.