The Holmes edition of D&D was the first one I personally bought. However, I was playing before then with some friends and I can only assume they were using the same edition.
I started out as a player. I was part of the usual clique of "nerds" in high school; we liked fantasy, science-fiction and computers. We would hang out during our free time at school talking about books, comparing which ones were the best, etc. We'd share computer code as we wrote various games (despite the fact games were disallowed on the school computer system).
A friend, one grade ahead of me, was friends with a person, one grade ahead of him. This friend had D&D. One day a couple of us were invited over his house after school to play some D&D. Needless to say we loved it. Thereafter you would see us playing during lunch and after school. During "senior skip-day" instead of heading out and getting drunk, we went to the local park and played D&D all day long.
From there I learned where we could find the books and anytime my mother was shopping in the same shop plaza, I'd spend my time at the shop (a camera and hobby shop) looking at the new books. I'd talk my mother into getting me selected rpg books which she did (though she had no idea what they were). I started with the Holmes edition and then the hardbound AD&D books. And then onto other rpg games.
My mother was a tax preparer on the side and she had a copy machine as part of that occupation. I remember making copies of all the books for my friends and we would share the books that way since we were too young to have much money ourselves. Fresh copies still reminds me of D&D to this day.