If you'd like a little background on these, there's a good interview that Chow gave over at Digital Arts.
Here's what he says about the Don Draper poster.
"Being a caricaturist, you are always looking for new people to try and capture. Don Draper seemed the perfect the person to illustrate because of his personality, the way he was dressed, his posture, his stance -- he is like a walking caricature anyway.
"When I finished the Don Draper caricature, it initially felt a bit out of context. I needed somehow to pin him down, so with the first episode being called Smoke gets in your eyes, I gave Don a cigarette and put the Lucky Strike logo behind him, and it just worked as a poster."
Also, here's the back story on the Joan Halloway poster. "The reason why I put the words 'Miss Holloway' over her boobs was obviously to emphasize Joan's assets, but it was also a little statement portraying how outrageous the sexism in that era and environment. I didn't feel I had to find anything extra to make the images work -- all the references I needed are all in the show."