There are many support groups for net addicts, most of them are on the Internet. I've found a web page called "www.helpguide.org" where you can find a lot of useful suggestions.
I think the most interesting advice is to replace your Internet time with healthy activities.
This addiction, according to the experts causes depression, stress, backache and headache.
I think experts consider Internet addiction a personal weakness, someone who is to shy or doesn't have much social life is more likely to become an Internet addict.