The Deathknights will be in the new expansion Wrath of the Lich King, You have to have a character of lvl 55+, you will not have to have a lvl 70, or lvl to 80 in order to make/unlock this new character, it will not replace your old characters at all, it will be like making a whole new character, but with the exception of starting at lvl 55, in there own area, they will get quests to get there own land riding mount, so the Deathknight mount will be free through a quest, you can lvl a Deathknight just the same as lvling your other characters up to lvl 80, even by going to Outland, the Deathknight starts in its own starting area, so for the first little bit it will not be Horde nor Alliance, but eventually betray The Lich king, and go Horde or Alliance, you cannot make a Orc Deathknight and go for ally, nor Human Deathknight and go for Horde, whatever reace you make will be for the same faction, I know most of this is just repeated over and over again, I just wanted to put my two cents in for whatever it is worth, and in hopes of clearing up the confusion. I hope this helps, and good luck with lvling your Main character upto lvl 80, as well as making your new Deathknight.

You can make a Death Knight out of Any race, but they do not serve Horde or Alliance, You have a completely separate starting area and you work with people such as Baron Rivendell (If you remember him from Stratholme).

You’re first few quests are to defeat failed Death Knights before Arthas himself.

And they are not overpowered as videos have shown, they are a unique class, since nobody will know how to use them – there is no fear of Death Knights owning anybody in a Battleground, Correct? – and I beleive that is what the new Battleground is about – 3 way chaos… Seige weapons, its a mad rush to claim 3 bases – the first to 3 wins…

Looks like its going to be fun.

You need to be level 55 to change into DK
You can be any race or class to change.

Thats all

Im kind of interested in this new profession, ‘Inscription’ which is like maming your own spells, so im guessing like little scrolls tht when clicked perform like a curse on the Mob.
Your best source is The WoW site, even though they tend to make it sound better than actually is.