I spose it depends how you describe 'addictive'... if you mean physical dependence, then marijuana is fairly benign - you can go through withdrawal if you suddenly stop taking it on a regular basis, and suffer from heavy night sweating, insomnia, bizarre vivid dreams when you finally do sleep, and a number of other withdrawal-type effects.
In terms of psychological dependence on the other hand, because marijuana can be incorporated into your daily routine, just like smoking cigarettes, it can seem like every time you turn around you think about having a bong/joint. This IMO is the hardest part to break yourself from. Going through THC withdrawal symptoms is piss easy compared to some other drug withdrawals, but you have to be firm to tell yourself "NO" every time you feel like having a pipe. If you want to stop yourself then I'd suggest either throwing out all remaining marijuana in your house, or electing to quit when you're out of supply. Then, you won't be able to smoke, unless you go out and buy some. Make sure you don't.
It will take willpower, and self-discipline, but it's really only the first couple of days that are difficult IMO because that's when you're copping the insomnia and night sweats, and you think you'll never be able to get to sleep without a pipe. Going complete cold turkey is a good way to stop this drug habit, because the withdrawals are not very harsh, and that way you avoid fooling yourself that you're going to stop 'tomorrow' and that 'one more cone to help you sleep tonight and then no more' will end up with you continuing to smoke until the choof is gone, and then you'll buy more, and you haven't quit at all.
It may help to figure out a reason or a motivation for quitting, which can give you something to remember why you're not smoking. Each time you think about smoking a bong, remind yourself of why you want to quit. Even if it's something as simple as telling all your friends (who know you smoke) that you've decided to go it clean and quit; hopefully if you make a strong stance on the issue then the thought of seeming weak-willed in your friends eyes may encourage you to stay off the pipe.
Hope that's some kind of help,
BigTrancer