Can anyone tell me about this Walmart scam?

I've been getting this persistent call from some guy with a foreign accent who says I won 2.5 million dollars. I can never catch the name of the company he is supposedly with but the word/words business or businesses???? is in the name of the "company". Anyway, he called the other day and announced that I won 2.5 mil and they would be delivering my money the next day. He asked me three or four innocuous questions but one kind of scared me--he knew with whom I lived. Not specifically the name of the person but still... Anyway, did not stay home the next day--of course--but then two days later he calls back and tells me I won a "grand prize package" from the same company and that they would be delivering it later that day with a lawyer and even someone from the Better Business bureau. He said I needed to purchase a Walmart card and when the people showed up at my door I was to show them the card, my drivers license and I think one more thing. He gives me all these code words or something I was to call him back and tell him when--either after they got there or after I bought the card. (I cannot remember which). I again hung up on him. He called a third time and I threatened him with harassment charges. I know it is a scam but out of curiosity what would have happened after they came to my door? What would these people have gotten out of me had I continued?