There's a couple other threads that go into Whole hog as well. Try a search for them. I know I've gone into some detail about doing them on a grill (I know thats not the same as in an underground oven, but the concept remains the same) I just can't remember which threads I posted it on.
I agree with YB that the underground method seems like alot of work, but I wouldn't let that discourage you. The wow factor is huge. The grilled method is sneakily simple.
Let us know how you make out.