I don't know of any really established DK tanking discussion sites at the moment, but.. It's a new class, it's going to take a little trailblazing. Get reading :P
Don't send him to the official WoW forums as it is a cesspool of idiocy. EJ has good info. Also on this site Gestalt made this thread which is very comprehensive on all aspects of the DK:
There is a thread called "Have a beta tester look at your spec" I posted a lot of my thoughts on tanking builds towards the end of that thread i think page 25+
Here is the thread my first tanking info starts mid page and goes till the end of the thread. Gestalt has a lot of good comments in that stretch as well. Read those 5 pages you'll learn a lot on why you should and shouldn't take different talents
I'm gonna go out on a limb and assume that for DK tanks your priorities for stats should be:
Stam>Str for base stats
Defense (till cap) then Dodge/Parry
As far as holding agro...throw out diseases when necessary...spam obliterate and frost strike...rune strike when it pops...taunt/etc. when necessary.
If you go looking for a maintankadin type site all you will get is a headache over the ridiculously long rotations and super specific specs which are just not needed to hold agro anymore...but they'll still act like they are.