So I just recently discovered this feature of Windows (and OSX).
I'd been trying to get internet on a few devices like my 360, and a desktop computer, that didn't have wireless adapters.
I didn't want to shell out for one (especially in the 360's case), and I didn't want to or sometimes couldn't run super long cables between rooms.
So after a bit of poking around, I came upon another solution that doesn't get talked about much.
ICS, or Internet Connection Sharing.
Basically, you use a computer that DOES get internet, to share it to other devices that don't.
But actually, I should first clarify that you don't want to ICS specifically on a Windows PC if you already have a router. ICS is when you plug one computer directly into the modem, and it does the job of router.
What you SHOULD do, is if you have a laptop with built in wireless, or a desktop with an existing wireless adapter, is BRIDGE it's wireless and wired connections. The PC acts as a bridge (a type of device you normally purchase separately), taking wireless internet in, and spitting WIRED internet out.
Laptops are especially helpful for this, as they almost all have built in wireless, and they can be set up right next to the devices that need to get online.
So now you can have a scenario like this:
Wireless router/access point in Room A.
Laptop or desktop with wireless adapter in Room B.
360 / Xbox / PS2 / (insert other device without wireless here) in Room B as well.
Attach 360 with ethernet cable to the laptop or desktop w/ wireless. Enable bridging.* Voila!
The downsides to this method are that the PC doing the bridging has to be turned on. And also that the device w/o wireless has to be somewhat close to the device w/ wireless - or else you just have the long cable problem again. Then again, perhaps you can deal with a long cable within one room, and not having to bore through walls to other rooms.
This way, I didn't have to spend $100 on the 360 adapter, the router could stay where it was (in another room to be attached wired to my desktop also in there), and I didn't have to buy a super long ethernet cable and drill through walls to get it from the 360 to the router.
*to enable bridging, go to network connections, select the two connections you want to bridge (it's LAN card and wireless adapter) and then right click - select bridge.
**Mac instructions - Can someone help me out here? I'm pretty sure there's just a application under sharing called "Internet"
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This one is cheaper, smaller and claims it can do more than just bridge: http://www.newegg.com/Product/Product.aspx?Item=N82E16833320025R No reviews, so this would be a shot in the dark.
Just something to think about. Sorry, I don't know specific instructions on how to set up bridging mode on OS X. I'll assume it involves configuration editing and/or the command line.
I just love not having to spend money at all and use an existing same room PC or a laptop. weeeeeee