The only thing that ever works for me is to.just.quit. Cold turkey. I have done this with tv, and after 2 years I can say I am pretty much cured.
: There was a time, early on, where I would fall back into the obsessive tv watching when I travelled for business (hotel tvs are my downfall - channel surfing from bed! with room service! JOY!). But the last time I travelled I didn't even WANT to turn it on. So I consider myself cured from tv (although I will occassionally watch a football game at a friend's house
Internet is another story. I have gone for (at most) a few days without getting online, even when I really resolve to take a break. It's so much harder to stick with it. So often I have a "legitimate" reason to get on ("I'll just check the weather, then get off"), but 6 hours later I'll find myself on some obscure blog, reading about knitting!
: I don't even knit!
I think it's probably the same thing as the tv. You just have to take a long enough break from it, and develop habits and hobbies that have nothing to do with a screen. Once you restructure your day-to-day, then you aren't so vulnerable to the lure of the easy passive entertainment. But it takes time, and you have to be willing (and able) to deny yourself the tv/internet for as long as it takes to build a new life. In my experience with tv, that took about 8 months. The thought of going 8 months without internet makes me want to hurl.
Sorry - this is clearly becoming a post that is more about my issues than yours!
But I do think that if you can cut out all the racket and distraction of the tv/internet, you'll figure out why you let it take you over in the first place...