How can I help my dad quit smoking?

I am eighteen years old and my dad, who is 44, has been smoking my whole life. For about five years now, he has been telling me and my mom that he doesn't smoke, but yesterday admitted that he's been lying the whole time. He claims he only smokes when he's "stressed out from work", but he spends about 12 hours a day at work so I don't know how many cigarettes he goes through. When I found out he never quit, I started having a panic attack. I am an only child and I am very close to m parents. I don't want to lose my dad because of something so preventable as smoking-related sicknesses. I expressed my feelings to my dad and he seemed touched and promised that he would stop but I feel like he doesn't have the resources and personal will to do it. He's very impulsive (probably smokes without thinking about it) and also avoids talking about things he doesn't feel comfortable about (quitting). I made the wallpaper on his laptop a picture of our family and I also switched the homepage of the internet from yahoo.com to www.smokefree.gov. Is there anything else that I can do to make him realize the urgency of his need to stop smoking?