Tethering on Windows 7?

A detailed step-by-step to setup wifi tethering/hotspot in Windows 7, Windows 8 WITHOUT any 3rd party software:

1. From admin Command Prompt type:

   netsh wlan set hostednetwork mode=allow ssid=mywifinetwork key=mysecretkey
   

2. Enable new virtual Wi-Fi adapter (it might be disabled upon creation)

3. From admin command prompt type:

   netsh wlan start hostednetwork
   

4. From current internet conection adapter share (ICS) internet to the new virtual adapter

5. Connect from wireless client to virtual SSID. Wi-Fi client gets an auto IP and you're good to go.

After host computer restart you only need to repeat steps 3 & 5 to be up and running.

Take a look at Connectify: http://connectify.me

Create an ad-hoc network. Here is the guide for Windows 7 from the Microsoft site. http://windows.microsoft.com/en-US/windows-vista/Set-up-a-computer-to-computer-ad-hoc-network

You could use the ad-supported Connectify app, as someone else mentioned, or use http://virtualrouter.codeplex.com/, or do it my hand with the netsh command and ICS with a little bit of effort:

netsh wlan set hostednetwork mode=allow ssid=YOURFRIENDLYSSID key=SOMEPASSWORD     
netsh wlan start hostednetwork

... then share the real connection through the virtual WiFi NIC.