Apple Software Base Station
Use an OS X machine with an AirPort card as a true access point.
Mac OS 9 had a handy AirPort feature called “Software Base Station.” It allowed any Mac with an AirPort card and an Ethernet (or dialup) connection to act like a hardware access point, sharing its Internet connection over the wireless. The early versions of OS X were noticeably lacking this handy feature, but it has been restored in OS X 10.2.
To begin, you need to establish a connection to the Internet over
something other than wireless (Ethernet is ideal). You might think
that to start a new wireless network, you could simply click on the
AirPort icon and select Create Network, but this
will make an
IBSS (peer-to-peer) network.
In order to turn your Mac into a true access point, you need to go to
System Preferences
→
Sharing, and click on the Internet tab, shown in
Figure 4-2.

Figure 4-2. Enable Software Base Station in the Sharing Control Panel.
Check the top box (Share your Internet connection with
AirPort-equipped computers), but before clicking the
Start button, you probably want to set up your
wireless parameters. Click the AirPort
Options... button, and you should see a drop-down menu
like that shown in Figure 4-3.

Figure 4-3. Set up your radio parameters under AirPort Options.
Specify ...