From what i have ead and its not guarenteed so dont take it all in.
Apparently the quest to obtain a dk will start roughtly around lvl 58 maybe higer. The quests that are involved to do this are going to be more or less the same style that you would have done to obtain the epic mount if you are a warlock.
Once that is done you get your dk. It comes with armour etc all you have to do is make it better.
As for the races im guessing they will do it on all races.