Intersting bits of info that are pouring in within the
Beta Forums:

Eryador@Hellfire:
You can go in now. First you have to complete a quest with a tourguide that shows you around. Its slow and boring, but whatever.

As stated before there are 3 instances: Old Hillsbrad, The Dark Portal and Mt. Hyjal.
You have to do them in order. What I mean is you cannot zone into Dark Portal without rescuing Thrall in Old Hillsbrad first. So I guess you cant zone into Mt. Hyjal without doing the other 2 first.

Old Hillsbrad is funny as hell. Dont go near Tarren Mills there are lvl 67 elites that will aggro.
Go to Southshore and and look at all the famous NPC’s!!!!

NPC’s I saw in Southshore:
Nat Pagle
Kel Thuzad
Herod (small boy named Herod the Bully)
Capt. Haines and Capt. Sanders (I think these are sailors from a Wetlands quest?)
Highlord Mograine
Tirion Fordring
Taelan Fordring
Stalvan (yes they guy from the Duskwood questline)
Mograine’s son (the one you have to find in Outland to get the Ashbringer)
Nathanos the Blightcaller

I saw some others but thats what I remember. Go there and have some fun

The not funny part is when you die you go to the Gadget GY. To go back into the instance is and INCREDIBLY LONG walk. Believe me getting to the caverns is the first part; the path going down to the instance it really, really long. Blizzard please put a GY closer to the caverns its way too long.

Tigole: “This instance is not supposed to be open until the next push. We’ll be closing it down shortly. It’s basically ready to go but QA found a showstopper bug at the last minute so we’re closing it off.

Also, we intend to add a closer graveyard. It just hasn’t been implemented yet.”