All the info about what will and won't be supplied with the 360 and launch can be found in this article on the home page
http://www.planetxbox360.com/?view=article&article=33
However to answer your questions
The Xbox 360 will include a headset in the standard package.
The wireless network adaptor is an optional extra and will cost you extra above the standard Xbox360 package. There have been no prices released yet for any accessories, so it's a case of just waiting for them to be announced nearer the launch.
As for the Live side of things, there are two packages available, Silver and Gold.
Silver is free and will allow players to share their Gamer Profile—comprised of user-generated information such as Achievements (rewards players have earned in games), Gamerzone (style of play), and a custom-created Gamertile (a visual icon to represents the gamer online)—with their friends in the community. And, with the free level of Xbox Live, players can send and receive text and voice messages to friends, as well as engage in Xbox Live voice chat anywhere, anytime, even if one person is playing a game while the other is watching a progressive-scan enabled DVD movie. Also available is the Xbox Live Marketplace, a one-stop shop to download demos and trailers along with new game levels, maps, weapons, vehicles, skins, community-created content, and more to the detachable Xbox 360 hard drive.
The premium package (Gold package) has all this and the thrill of multiplayer online gameplay 24hours a day, 7 days a week. Other Xbox Live features for premium members include video messaging, online tournaments and ladders, and exclusive, original programming such as playing with celebrities online and joining sponsored tournaments to win prizes. There has been announcement on price for this yet, but assumption is it'll be no more than what the current 12 month subscription is now.
On a side note all Xbox 360 owners who sign on to Xbox Live for the first time can kick-start their experience with a free month of the full (premium/Gold) subscription service, which will let them experience the full power of Xbox Live.
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