Can someone please tell me which episodes any one of the characters appear before 1900 in both series?  They don't have to be together at the same time either--it can just be when Darla is turned, and so forth.  Anyway, I need all episodes with those four characters.

Thanks in advance

Well, Fool for Love and Darla I know were two of them. Then there was Lies My Parents Told Me and Destiny and the Girl In Question. That's all I can remember.

There's a really great resource that lists the entire history of the Fanged Four with references to each episode the characters either appeared in or information about them was revealed. AtS was generally chock full of flashbacks during seasons 1-3. You'll find multiple scenes with either Angelus or Angelus and Darla together throughout the series. There were also flashbacks in AtS: 4 when the fang gang has to confront The Beast and we get glimpses of Angel in Vienna.

Here's the link for your reference. It might take some purusing, but it's very thorough and lists every episode: http://peasant.notanothersite.com/gate/history.html

Also, Amends, BtVS season 3, the one with the First Evil. But I think ClawofCat's link is your best bet.

If you need to watch the scenes, some patient soul has put them all together and put them on youtube: http://ie.youtube.com/user/effulgent12.

I haven't watched the whole thing, but I think it's around 2 hours long. Even though it's called "The Vampire Angel," it starts with Darla's turning, and goes chronologically through every single flashback involving any one of the Fanged Four up until Angel sees Buffy on the school steps in L.A.

Oh wow...thanks so much you guys!  And two hours?  Well, I've got time