How do I make my Xbox 360 wireless using a wireless network and a router instead of the expensive Xbox adapter?

If you have a laptop: try this.

Connect the laptop too your xbox with some CAT 5 cable (eithernet cable).
then go to your control pannell on your laptop and make sure that it can share its connection with other computers. you should be able to connect then. plz best answer me

uhm. . . I’m not sure. . . but i think this could help.
I have an Xbox360 too, and mii mom and i use an ethernet cable (itz likka yellow cord that you connect from the Xbox to the router).
I think it could work. If not, sorry. . .
I don’t know that much about it.
Sorry!

Here’s the answer to your question:

HOW TO: Cheap Wireless For Your Xbox 360
http://www.geeksaresexy.net/2007/10/02/how-to-cheap-wireless-for-your-xbox-360/

The 360 must go online using something plugged into either the Ethernet or USB port on the back. That being said we can begin to narrow down our options: 1 if you want to get the most bang for your buck, you should do whatever you can to wire it directly to your router, it’ll definitely give you the best performance. There are other devices that can receive a wireless signal much like the official Xbox360 wireless adapter does. Unfortunately, most of them are just as expensive as the official adapter is, and there’s no guarantee that they;ll work. Your only other option then is something that does not technically use wireless, but doesn’t require a direct line from the router…this is where it gets pretty specific. And this is pretty much your only other option. These things are called PoE adapters (Power over Ethernet) these things actually work pretty well. They come in two parts, the first part you plug from you router to any standard wall outlet. Then the device uses your buildings wiring to transfer the connection to the second device that is plugged in between your Xbox and another wall outlet. It works just like a wired connection, but without having to run new wiring. The problem here again: Cost. These run anywhere from $30-$100 depending on where you get them.
So sorry, but these are your only alternatives to just buying the wireless adapter (as far as I know). To review, your 3 options are: Wired (through a standard Ethernet cable, which will run you between $10 and $30 depending on length), wireless (which is less reliable and more pricey, but saves a lot of trouble) or Poe (which is more reliable than wireless, but just as expensive, and most models take up a power outlet, and it requires that you have direct access to your wireless router). Good luck!