There wasn't a lot to it, just grunt work.
Steve and I submitted under different usernames (no comments back then) but it was entirely manual. Most of the submissions were from "kn0thing" and "spez" but from time to time we'd submit as a different username, to give the appearance of a 'live' site (nothing sadder than an empty reddit).
The first real users after friends and family came after PG linked to us in an essay, fortunately a number of them stuck around and (1% rule) some even started submitting.
I exhausted bloggers pretty equally and back in 2005 there weren't any options beyond that for getting the word out -- just facebook.
What a difference 5 years made. It made launching hipmunk so much easier.
Like HN, I often don't even bother with the linked article because the comments usually have so much more value. I think there's even more value to be extracted there if one can find a way to bump back up the S/N ratio....
I'm a big fan of HN, though I do wish /r/startups would grow into a similar community.