I needed a Wireless Internet connection at the office to connect my phone so I could update it, none was available so I created my own Access Point. I used my iMac's Airport as an AP. My iMac's is connected to the internet using Ethernet. Here is how you do it:
1. Click on the Apple logo on the upper left corner of your screen > Select "System Preference", A window will pop out.
2. Under "Internet & Wireless" Click on "Sharing"
3. Check the box beside "Airport" and click on the "Airport Option"...
5.) Now put a check beside "Internet Sharing" to start your "Airport". A warning will pop up, just click on "Turn Airport On". Clicking it will make another dialogue box pop up asking if you are sure. Just click "Start" and that's it. You've made your mac an Access Point. Now give yourself a pat on the back.
Note: If this setup suddenly stops working or started having problems after auto updating your Mac to ver. 10.6.7 simply download the full 10.6.7 combo patch from apple and install it. You can google this filename "MacOSXUpdCombo10.6.7.dmg" so you can find it easily. Restart your Mac after patching and your good to go. Airport will work again as it should.