@Steak: Take a look at these vids [link]http://www.youtube.com/watch?v=klXolslGsk4&feature=related[/link], they have been invaluable in me learning and surviving the game, plus the guy says some funny things now and again.
@Lost: I think four hours might be pushing it a little, but you never know, if I'm still awake at five am I'll get in touch.
Also, are they dieing from failed strange moods/melancholy from friend deaths? I've had a couple go that way, though the biggest killer in my fortress is a bridge I have to retract when I get invaded from the caverns, however when it retracts, anyone on the bridge falls five z-levels, shatters their spine and then suffocates due to full body paralysis, currently its claimed about 7 Dwarfs and counting.