Is it addictive? Hell yes.
I've smoked for years, since I was in my early/mid teens (awful, I know). I quit for 3 months last year and it was damned hard work. Took it up again after a moment of stupidity and have been "serial quitting" ever since. Quitting, relapsing, quitting, relapsing, repeat ad-infinitum. (Things I have learned this year: you can never have just one). Currently back into a quit and hoping that this will be the last one.
Yes, there are physical withdrawal symptoms. Some people feel them more than others, I know I did.
That said, I also agree with Stewart in that alot of it *is* psychological. It's not easy to give up, but it is very simple. Learning to break the skewed association between smoking and pleasure is probably the hardest, and most important part of any quit. I say skewed, because most smokers think they enjoy smoking - but actually, it's more that they don't enjoy not smoking. The "pleasure" aspect comes purely from the relief of withdrawal symptoms (physical, or psychological, whatever) that occurs when you light up. That was a big revelation to me when I quit.
Once you've got the pleasure association part licked, you're alot more in control of it. I hate medications as a rule, but NRT can be pretty handy in this respect - learning to break the habit element while not feeling too many physical symptoms of nicotine withdrawal. *Then* you handle the weaning-yourself-off bit once the habits are broken, by which time hopefully the psychological desire to smoke is less. Makes it a bit less rough.
One of the hardest parts, and I'm speaking from experience here, is being on your guard against relapsing. Knowing what your triggers are, and making plans to deal with them in advance, is essential. That's usually where I fall down. And this definitely *isn't* physical.